Physical Activity and Body Composition Outcomes of the “Primary School as a Whole-Day School” Program in Early School-Age Children from Croatia

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I appreciate the opportunity to review this well-structured and relevant manuscript addressing the impact of a whole-day school program on physical activity and body composition in Croatian primary school children. The topic is timely and aligned with current efforts to evaluate system-level educational reforms promoting children’s health.
However, several sections of the manuscript require clearer alignment between the reported statistical results and their interpretation, as well as a more concise presentation of methods and discussion. In particular, the statistical approach, data presentation, and proportionality of the discussion should be revised to strengthen the scientific rigor and clarity of the work.
Please find my detailed comments below, organized by section.

Lines 48–57
The text accurately describes the coexistence of low physical activity and high overweight prevalence, but the causal or theoretical link between PA, motor competence, and obesity risk isn't clearly explained. Please add 1-2 sentences explicitly detailing how increasing Physical education frequency is expected to influence both PA levels and body composition, such as through increased MVPA time, improved motor competence, or behavioral reinforcement.

Lines 92–99
Authors mention that “…only one study has evaluated…” but do not specify what that study found, its methodological limitations, or how the present study extends it. Without that, the novelty claim feels weak. Please summarize the prior study’s outcomes and limitations

Lines 97-98
In these lines, the authors explicitly present only one aim, formulated as a broad evaluation of the program’s effects on PA and body composition. However, the abstract specifies two distinct aims. Please check and correct.
Delete lines 103-107 entirely. If the authors wish to preserve the ideas, they can move them to the final paragraph of the Discussion or conclusion.

Participants and study design

This section is too long. Please condense this section into fewer paragraphs.
Lines 110-122
The design is described as “comparative observational” and later as “quasi-experimental,” which is inconsistent. A quasi-experimental pre–post design with non-randomized groups cannot be simultaneously labeled “observational.
Authors should clarify the study design.This was a quasi-experimental pre–post study with non-randomized group assignment
The sample description omits important details about school selection, sampling frame, and justification of the sample size.
There is no mention of how many schools were included, or whether clustering by school was accounted for statistically.
The section does not specify any individual-level inclusion or exclusion criteria for participants. The only criteria mentioned (lines 135–137) concern school selection, not the children themselves.
Please indicate:
1.    how participants were recruited within schools,
2.    whether all students in selected grades were eligible,
3.    any exclusion criteria (e.g., health conditions, incomplete accelerometer data, missing parental consent),
4.    and the final number included after applying these criteria.
•While the program “Primary School as a Whole-Day School” is described in detail, the section reads more as policy information than as an intervention protocol. There is no description of fidelity, implementation monitoring, or exposure quantification (e.g., how many PE lessons each child actually attended, or whether extracurricular sessions were standardized). Please make a specific section of  “intervention” and briefly summarize the intervention in terms of components, duration, frequency, and responsible personnel, rather than administrative structure.
•Confirm whether the same protocols, staff, and devices were used at both time points to ensure measurement reliability.
•Figure 1 is helpful, but it omits critical details about sample sizes, attrition, and measurement timing (duration of accelerometer wear, number of valid days, etc. Please consider revising Figure 1 or including an additional flow diagram (CONSORT-style) showing participant inclusion, attrition, and missing data handling

Variables
The technical description is solid, but several methodological aspects are missing for reproducibility: Epoch length, non-wear time criteria, minimum valid days, and intensity cut-points are not specified. These are essential for PA research in children and directly affect comparability across studies. Please include this information. 
Regarding PAQ-C questionnaire, authors made an dequate description, but the rationale for combining direct (accelerometer) and indirect (PAQ-C) measures is missing. It’s unclear whether the questionnaire served for triangulation, validation, or as a complementary variable.

Statistical analysis 
There’s also no mention of homogeneity of variances (Levene’s test) or sphericity (Mauchly’s test), both of which are necessary in mixed ANOVA designs. Please add the information.
A mixed ANOVA assumes balanced cell sizes and homogeneity of covariance matrices (Box’s M test), which were not mentioned. Pleasse clarify. Moreover, add a statement about effect size reporting (e.g., partial η² for ANOVA, Cohen’s d for pairwise contrasts).
Authors run separate ANOVAs for each dependent variable rather than a MANOVA. Thus, all dependent variables were analyzed separately. However, the section does not mention a correction for multiple dependent variables. Without FDR or Bonferroni control, the risk of type I error inflation is high. Please correct the analysis.

Results
There is an inconsistency in how decimals are presented throughout the tables. In some cases, decimals are separated by dots while in others, commas are used. Please ensure consistency in the decimal notation according to the journal’s English formatting standards.
Table 1
•SDs are inconsistent in decimal precision (some with 2 decimals, others with 1).
•There are no statistical indicators (e.g., p-values, effect sizes) for pre–post differences. What is the rationale?
Table 2
•Effect sizes (partial η²) are missing.
•What is the meaning of “*” in the table?

Tables 4 and 5
The inclusion of separate tables for boys and girls is not clearly justified statistically. According to Table 2, no significant Time × Group × Gender interactions were found for most variables, which suggests that gender did not moderate the intervention effects. Presenting stratified results by gender without significant interactions may lead to redundant or potentially misleading interpretations.
I recommend either removing these tables or, if the authors consider the sex-specific data important for descriptive purposes, briefly summarizing them within the text and clarifying that no statistical interaction was observed. This would improve clarity and avoid overinterpretation while maintaining transparency in reporting.

Discussion
While the Discussion is comprehensive, it could be made more concise by summarizing overlapping explanations and focusing primarily on the statistically significant outcomes. Condensing this section would enhance readability and strengthen the emphasis on the study’s main contributions.
Lines 289-330
•The discussion of environmental and behavioral factors (weather, school calendar, PE frequency, teacher specialization) is reasonable and grounded in literature. However, this section repeats too much context already described in the Introduction (e.g., specialized teachers, increased lesson frequency). These explanations could be summarized rather than restated.
In addition, the link between the number of PE lessons and MVPA increase is assumed but not statistically tested, and the idea that “weather conditions influenced results” is speculative and should be framed as a limitation, not as an explanatory argument. Overall, i suggest condensing the first two paragraphs, integrating the role of PE teacher specialization with literature support, and removing repetitive contextual material. Clarify which findings were statistically significant before proposing explanatory mechanisms.

Lines 353-375
Authors appropriately focus on MVPA, which showed a significant Time × Group × Gender interaction. However, another significant three-way interaction was also observed for STEPS (Table 2), but this result is not addressed in the discussion. It would strengthen the interpretation to briefly discuss whether the STEPS outcome followed a similar pattern to MVPA and whether both indicators suggest consistent gender-specific responses to the intervention. Additionally, quantitative context (e.g., magnitude of change or effect size) would enhance the interpretation of these differences.
Lines 377-406
The reasoning regarding insufficient intervention duration and growth-related confounding is sound. Likewise, the mention of nutrition as an uncontrolled factor is appropriate and well justified. However, this section of the discussion could be more balanced by acknowledging the measurement limitations of bioimpedance in growing children (hydration sensitivity, diurnal variation).
Line 419
Please rephrase the sentence: “our results, although not being the final Word…”
Lines 422-445
•This section is well-written, transparent, and well-balanced. However, it misses one important point: a Lack of correction for multiple comparisons. This must be acknowledged.

Author Response

REVIEWER 1

 

Comments and Suggestions for Authors

I appreciate the opportunity to review this well-structured and relevant manuscript addressing the impact of a whole-day school program on physical activity and body composition in Croatian primary school children. The topic is timely and aligned with current efforts to evaluate system-level educational reforms promoting children’s health.

However, several sections of the manuscript require clearer alignment between the reported statistical results and their interpretation, as well as a more concise presentation of methods and discussion. In particular, the statistical approach, data presentation, and proportionality of the discussion should be revised to strengthen the scientific rigor and clarity of the work.

Please find my detailed comments below, organized by section.

RESPONSE: We thank the reviewer for the thorough evaluation of our manuscript and for recognizing the relevance and timeliness of the topic. We appreciate the constructive feedback and the clear guidance provided. In the revised version, we have improved the alignment between statistical results and their interpretation, clarified and streamlined the Methods section, and adjusted the Discussion to ensure a more concise and focused presentation. Detailed, point-by-point responses are provided below.

 

Lines 48–57

The text accurately describes the coexistence of low physical activity and high overweight prevalence, but the causal or theoretical link between PA, motor competence, and obesity risk isn't clearly explained. Please add 1-2 sentences explicitly detailing how increasing Physical education frequency is expected to influence both PA levels and body composition, such as through increased MVPA time, improved motor competence, or behavioral reinforcement.

RESPONSE: Thank you for this valuable suggestion. We agree that the theoretical link between physical activity, motor competence, and obesity risk should be stated more explicitly. In the revised manuscript, we have added 1–2 sentences in the Introduction to clarify how increasing the frequency of physical education is expected to enhance MVPA, support the development of motor competence, and consequently contribute to healthier body composition. These additions strengthen the conceptual foundation of the study. Text now reads: “Increasing PE frequency provides additional structured opportunities to accumulate MVPA, which is associated with healthier weight trajectories in childhood [13]. Moreover, regular participation in PE supports the development of motor competence, a factor that promotes higher PA engagement and reduces long-term obesity risk [17,18]. Together, these mechanisms explain how enhanced PE provision may influence both PA levels and body composition.”

 

Lines 92–99

Authors mention that “…only one study has evaluated…” but do not specify what that study found, its methodological limitations, or how the present study extends it. Without that, the novelty claim feels weak. Please summarize the prior study’s outcomes and limitations

RESPONSE: Thank you for this insightful comment. We agree that our original description of the previous study lacked sufficient detail to support the novelty of our work. In the revised manuscript, we now provide a concise summary of the findings and limitations of the study by Gerovac et al. (2025). Specifically, we note that the study demonstrated improvements in motor skill performance among children taught by specialist PE teachers, but was limited by its short duration, small sample size, and the absence of physical activity or body composition outcomes. We have incorporated this clarification into the Introduction to more clearly position the contribution of the present study. Text reads: “To the best of our knowledge, only one study has evaluated the effects of experimental schooling, showing promising effects of an experimental program on the acquisition of motor skills in early school-aged children [24]. That study reported improvements in motor skill performance among children taught by specialist PE teachers; however, the study was short in duration (i.e., three months) and did not assess PA or body composition outcomes [24].” (please see beginning of the last paragraph of the Introduction).

 

Lines 97-98

In these lines, the authors explicitly present only one aim, formulated as a broad evaluation of the program’s effects on PA and body composition. However, the abstract specifies two distinct aims. Please check and correct.

RESPONSE: Thank you for pointing out this inconsistency. We agree that the formulation of the study aim in the Introduction did not fully reflect the two aims presented in the Abstract. In the revised manuscript, we have updated the wording in lines 97–98 to clearly state both aims: (i) to evaluate the effects of the experimental program on physical activity and (ii) to assess its effects on body composition. This correction ensures full alignment between the Abstract and the Introduction.

 

Delete lines 103-107 entirely. If the authors wish to preserve the ideas, they can move them to the final paragraph of the Discussion or conclusion.

RESPONSE: They are now deleted, thank you for the suggestion.

 

Participants and study design

This section is too long. Please condense this section into fewer paragraphs.

Lines 110-122

The design is described as “comparative observational” and later as “quasi-experimental,” which is inconsistent. A quasi-experimental pre–post design with non-randomized groups cannot be simultaneously labeled “observational. Authors should clarify the study design. This was a quasi-experimental pre–post study with non-randomized group assignment

RESPONSE: We changed that inconsistency throughout the manuscript, thank you. It is now specified as “This study employed a natural experiment design with non-randomized group assignment to examine differences in outcomes between participants enrolled in two distinct types of schooling (whole-day schooling group and the regular schooling group), without any researcher-imposed intervention as it evaluates the effects of a naturally occurring policy-driven exposure.” (please see beginning of the Methods section)

 

The sample description omits important details about school selection, sampling frame, and justification of the sample size.

There is no mention of how many schools were included, or whether clustering by school was accounted for statistically.

RESPONSE: Thank you for your observation. In this version we paid special attention on mentioned and amended the manuscript accordingly. Text reads: “Since controlling the environmental effects on PA was highly important for the purpose of the study (i.e. environment can significantly influence PA in children), we specifically selected one school for experimental program, and one similar school for control program. Specifically, in the Split-Dalmatia county where the study was performed, only three schools were included in Whole Day School project, of which one was located on the island with limited resources (no educated PE teacher, please see later for details on program), and another one with <30 children involved in program. Therefore, the selected experimental school was most appropriate, both because of the geographical location, and number of participating children.” (please see Methods for newly added details and explanations).

 

 

The section does not specify any individual-level inclusion or exclusion criteria for participants. The only criteria mentioned (lines 135–137) concern school selection, not the children themselves.

Please indicate:

1.    how participants were recruited within schools,
2.    whether all students in selected grades were eligible,
3.    any exclusion criteria (e.g., health conditions, incomplete accelerometer data, missing parental consent),
4.    and the final number included after applying these criteria.

RESPONSE: Thank you for your suggestion. We added details you have asked for, and text reads: “All 3rd and 4th graders from selected schools were invited to participate, and parental consent was obtained before the study. The children involved in the study were healthy and regularly participated in the PE classes, while the great majority of them were involved in out-of-school sport programs during the course of this study (74% and 77% of the children in the experimental and control groups, respectively), with no significant difference between the study groups in out-of-school sport involvement. Inclusion criteria included: no health conditions which could prevent children from participating in PE classes, less than 20% of absence from school over the study peri-od, participation in the pre- and post-measurement, parental consent for the partici-pation in the study. Exclusion criteria included health conditions which limited par-ticipation in PE, more than 20% school absences during the study period, non-participation in pre-, or post-testing. Initially, 140 children were tested at pre-testing while post-testing involved 138 children. However, because of the non-meeting inclusion criteria, and necessity of paring pre- and post-testing results, the final sample included altogether 128 children (54 and 74 in experimental, and control group, respectively).” (please see Methods).

Also, we must note that in this version of the manuscript we added flow diagram of the study (newly added Figure 1)

• While the program “Primary School as a Whole-Day School” is described in detail, the section reads more as policy information than as an intervention protocol. There is no description of fidelity, implementation monitoring, or exposure quantification (e.g., how many PE lessons each child actually attended, or whether extracurricular sessions were standardized). Please make a specific section of  “intervention” and briefly summarize the intervention in terms of components, duration, frequency, and responsible personnel, rather than administrative structure.

RESPONSE: Thank you for this important observation. We agree that the original description of the “Primary School as a Whole-Day School” program contained excessive policy-level details and did not sufficiently present the intervention in terms of its components, duration, frequency, or delivery. In the revised manuscript, we have added a dedicated “Intervention” subsection that summarizes the program as an intervention protocol, including information on PE lesson frequency, responsible personnel, and children’s exposure to structured and unstructured PA components. Although fidelity and attendance could not be monitored at an individual level due to the nature of the national program, we now explicitly state this limitation. This restructuring improves clarity regarding what elements of the program may have influenced the observed outcomes.

Also, the differences between school programs observed are summarized in the newly added table (please see Table 1)

 

• Confirm whether the same protocols, staff, and devices were used at both time points to ensure measurement reliability.

RESPONSE: The statement is now added in the text, text reads: The same measurement protocols, staff, and devices were used at both time points to ensure measurement reliability.

 

• Figure 1 is helpful, but it omits critical details about sample sizes, attrition, and measurement timing (duration of accelerometer wear, number of valid days, etc. Please consider revising Figure 1 or including an additional flow diagram (CONSORT-style) showing participant inclusion, attrition, and missing data handling

RESPONSE: As you suggested in this version of the manuscript we included flow diagram (please see newly added Figure 1)

 

 

 

Variables

The technical description is solid, but several methodological aspects are missing for reproducibility: Epoch length, non-wear time criteria, minimum valid days, and intensity cut-points are not specified. These are essential for PA research in children and directly affect comparability across studies. Please include this information.

RESPONSE: Thank you for highlighting the need for additional methodological detail. In the revised manuscript, we now provide information on wear-time criteria, valid days, and data-processing procedures to improve reproducibility. Regarding epoch length, we did not specify this parameter because GENEActiv devices record raw triaxial acceleration continuously, and the GGIR package extracts activity metrics without the use of predefined epochs. Participants with non-wear periods were excluded from the analyses, and only those with at least four valid days (including a minimum of two weekdays and two weekend days) were retained. Intensity classifications (e.g., LPA, MVPA) were derived directly from the GGIR algorithm, which applies established, device-specific cut-points internally; therefore, manual intensity threshold selection was not required. All of these information has now been added to the Methods section to enhance clarity and comparability.

 

Regarding PAQ-C questionnaire, authors made an dequate description, but the rationale for combining direct (accelerometer) and indirect (PAQ-C) measures is missing. It’s unclear whether the questionnaire served for triangulation, validation, or as a complementary variable.

RESPONSE: Thank you for this helpful comment. We agree that the rationale for including both direct (accelerometer-based) and indirect (PAQ-C) measures of physical activity was not sufficiently articulated. In the revised manuscript, we clarify that the PAQ-C was used as a complementary measure to capture broader contextual aspects of children’s activity that are not fully reflected in accelerometer data (e.g., activity during organized sport, recess, or PE), and also partly for triangulation purposes. Including both instruments allowed us to examine whether perceived changes in PA (PAQ-C) corresponded to objectively measured changes (particularly in MVPA), thereby strengthening the interpretation of behavioral patterns. This explanation has now been added to the Methods section, and text reads: “The PAQ-C was included as a complementary measure to accelerometry in order to capture contextual and self-perceived aspects of children’s PA that are not fully re-flected in device-based metrics. Additionally, its use allowed partial triangulation with accelerometer-derived outcomes, enabling us to examine whether subjective in-creases in PA corresponded with objectively measured changes in MVPA.” (please see Variables subsection, 2^nd paragraph).

 

Statistical analysis

There’s also no mention of homogeneity of variances (Levene’s test) or sphericity (Mauchly’s test), both of which are necessary in mixed ANOVA designs. Please add the information.

A mixed ANOVA assumes balanced cell sizes and homogeneity of covariance matrices (Box’s M test), which were not mentioned. Pleasse clarify. Moreover, add a statement about effect size reporting (e.g., partial η² for ANOVA, Cohen’s d for pairwise contrasts).

Authors run separate ANOVAs for each dependent variable rather than a MANOVA. Thus, all dependent variables were analyzed separately. However, the section does not mention a correction for multiple dependent variables. Without FDR or Bonferroni control, the risk of type I error inflation is high. Please correct the analysis.

RESPONSE: Thank you for your comments. In this version of the manuscript we paid special attention on adding details with regard to statistical analyses. The statistics are now specified as follows: “All variables were examined for normality of distribution using the Kolmogorov–Smirnov test. Descriptive statistics were computed and are reported as means and standard deviations for continuous variables, and as frequencies and percentages for categorical variables (e.g., gender and grade). A 2 × 2 × 2 mixed-design analysis of variance (ANOVA) was conducted to exam-ine the effects of time (pre- and post-measurement; within-subjects factor), group (ex-perimental vs. control), and gender (male vs. female; both between-subjects factors) on each dependent variable. The assumption of homogeneity of covariance matrices was tested using Box’s M test, and equality of error variances was assessed via Levene’s test. Cell sizes were reviewed for approximate balance across conditions. Effect sizes were reported using partial eta squared (η²) for ANOVA main and interaction effects. For significant effects, post hoc comparisons were conducted using Scheffé’s test, and Cohen’s d was reported to quantify the magnitude of pairwise differences. Each dependent variable was analyzed separately using univariate ANOVAs. To control for potential inflation of Type I error due to multiple comparisons, a Bonferro-ni correction was applied across tests. All analyses were performed using Statistica v14.5 (TIBCO Inc., Palo Alto, Cali-fornia, USA). The threshold for statistical significance was set at p < 0.05.” (please see subsection on statistics)

 

Results

There is an inconsistency in how decimals are presented throughout the tables. In some cases, decimals are separated by dots while in others, commas are used. Please ensure consistency in the decimal notation according to the journal’s English formatting standards.

Table 1

• SDs are inconsistent in decimal precision (some with 2 decimals, others with 1).
• There are no statistical indicators (e.g., p-values, effect sizes) for pre–post differences. What is the rationale?

Table 2

• Effect sizes (partial η²) are missing.
• What is the meaning of “*” in the table?

RESPONSES: The results are amended accordingly. Specifically,

• SDs are reported consistently (one decimal only),
• effect sizes (as partial eta squared) are added in table (and statistical subsection) and interpreted accordingly
• symbols are specified in all table legends.
• we specified t-test differences between pre- and post-measurement for the total sample, and results are reported in Table 1.

 

Tables 4 and 5

The inclusion of separate tables for boys and girls is not clearly justified statistically. According to Table 2, no significant Time × Group × Gender interactions were found for most variables, which suggests that gender did not moderate the intervention effects. Presenting stratified results by gender without significant interactions may lead to redundant or potentially misleading interpretations.

I recommend either removing these tables or, if the authors consider the sex-specific data important for descriptive purposes, briefly summarizing them within the text and clarifying that no statistical interaction was observed. This would improve clarity and avoid overinterpretation while maintaining transparency in reporting.

RESPONSE: Thank you for your suggestion. Indeed, time x group x gender interaction was not significant for most of the variables, but we believe that presenting separate statistics for boys and girls was important because of the significant effect for MVPA, which was later discussed. However, in this version of the manuscript we clearly stated it in the Results section as you suggested. Text reads: “Despite the relatively small number of significant interaction effects, for the purpose of the specific interpretation of the overall effects, the changes between pre- and post-measurement were analyzed specifically for boys and girls.” Thank you.

 

Discussion

While the Discussion is comprehensive, it could be made more concise by summarizing overlapping explanations and focusing primarily on the statistically significant outcomes. Condensing this section would enhance readability and strengthen the emphasis on the study’s main contributions.

Lines 289-330

• The discussion of environmental and behavioral factors (weather, school calendar, PE frequency, teacher specialization) is reasonable and grounded in literature. However, this section repeats too much context already described in the Introduction (e.g., specialized teachers, increased lesson frequency). These explanations could be summarized rather than restated. In addition, the link between the number of PE lessons and MVPA increase is assumed but not statistically tested, and the idea that “weather conditions influenced results” is speculative and should be framed as a limitation, not as an explanatory argument. Overall, i suggest condensing the first two paragraphs, integrating the role of PE teacher specialization with literature support, and removing repetitive contextual material. Clarify which findings were statistically significant before proposing explanatory mechanisms.

RESPONSE: Thank you for this constructive feedback. We agree that the Discussion contained overlapping explanations and repeated contextual information already presented in the Introduction. In the revised manuscript, we have condensed the first two paragraphs, removed redundant descriptions of PE frequency and teacher specialization, and focused more clearly on statistically significant findings before discussing potential mechanisms. We also reframed weather- and calendar-related influences as possible limitations rather than explanations. The revised section now presents a more concise and focused interpretation of the results while maintaining appropriate links to relevant literature.

 

 

Lines 353-375

Authors appropriately focus on MVPA, which showed a significant Time × Group × Gender interaction. However, another significant three-way interaction was also observed for STEPS (Table 2), but this result is not addressed in the discussion. It would strengthen the interpretation to briefly discuss whether the STEPS outcome followed a similar pattern to MVPA and whether both indicators suggest consistent gender-specific responses to the intervention. Additionally, quantitative context (e.g., magnitude of change or effect size) would enhance the interpretation of these differences.

RESPONSE: Thank you for your suggestions. First, with regard to variable STEPS and significant interaction effect you mention. Indeed, there was statistical significance for Time × Group × Gender interaction, but this was a result of differences between boys and girls, while no statistical effect was found for Group, and/or Time. Therefore, we believe that the interaction effect was not important for our study aim and was not interpreted. However, if you would insist on interpreting it, we will surely follow your suggestion, please let us know. Second, with regard to interpretation of ES we followed your suggestion and briefly presented it in discussion as well. Thank you.

 

 

Lines 377-406

The reasoning regarding insufficient intervention duration and growth-related confounding is sound. Likewise, the mention of nutrition as an uncontrolled factor is appropriate and well justified. However, this section of the discussion could be more balanced by acknowledging the measurement limitations of bioimpedance in growing children (hydration sensitivity, diurnal variation).

RESPONSE: Thank you for this valuable comment. We agree that acknowledging the measurement limitations of bioimpedance analysis (BIA) in children is important for providing a balanced interpretation of the null findings related to body composition. In the revised manuscript, we have added a brief statement highlighting known BIA limitations—such as sensitivity to hydration status and diurnal variation—which may be amplified during periods of rapid growth. We believe that this addition strengthens the transparency of our methodological considerations and further contextualizes the absence of significant body composition changes. Text reads: “A further consideration is the inherent limitation of bioimpedance analysis (BIA) in pediatric populations. BIA estimates are influenced by hydration status, recent food and fluid intake, and diurnal variation, all of which can alter conductivity and affect accuracy. These sources of variability may be amplified in growing children, poten-tially masking subtle changes in body composition despite standardized measurement procedures [47]. Such measurement sensitivity should be considered when interpret-ing the absence of significant body composition effects.” (please see end of the 2^nd subheading of the Discussion).

 

Line 419

Please rephrase the sentence: “our results, although not being the final Word…”

RESPONSE: Thank you for pointing this out. We have rephrased the sentence to ensure clearer and more formal academic language.

 

Lines 422-445

• This section is well-written, transparent, and well-balanced. However, it misses one important point: a Lack of correction for multiple comparisons. This must be acknowledged.

RESPONSE: Thank you for this important observation. We agree that the absence of correction for multiple comparisons represents a methodological limitation. In the revised manuscript, we have added a statement acknowledging that the number of statistical tests increases the risk of Type I error and that future studies with larger samples should incorporate appropriate adjustments.

 

 

Thank you for your suggestions once again. Staying at your disposal!

 

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents an interesting and relevant contribution to the field of school-based physical activity promotion, examining how participation in a Whole-Day School program relates to changes in physical activity and body composition among Croatian children. The topic is timely and aligned with international efforts to evaluate the health impact of educational reforms. The paper is well written, and the use of objective (accelerometry) and subjective (PAQ-C) measures is a methodological strength.

However, several aspects require clarification and improvement to enhance the methodological rigor, transparency, and scientific impact of the study:

 

Line 38–39 (Introduction): Add citations to support the statement “Physical activity (PA) during childhood plays a vital role in supporting healthy growth and development.”

 

Line 41–42 (Introduction): The phrase “many children worldwide still fall short of the recommended 60 minutes of moderate-to-vigorous PA each day” is too vague. Include specific global or regional data.

 

Line 59–60 (Introduction): Add citations to support the statement “Indeed, PE has been widely recognized as an important setting for increasing children’s PA levels and reducing the risk of being overweight and obesity.”

 

Line 71–107 (Introduction): This section devotes extensive detail to describing the Croatian educational reform and its administrative structure, which weakens the scientific focus of the introduction. The justification currently rests mainly on the absence of local evidence, but it should also reflect what is already known internationally about the effects of similar whole-day or school-based physical activity programs. Incorporating findings from other countries would strengthen the rationale, demonstrate awareness of the global evidence base, and clarify how this study adds new or complementary knowledge rather than addressing a purely national gap.

 

Line 115–118 (Materials and Methods)
The terminology used to describe the study groups could be misleading. Referring to participants as belonging to an “experimental group” suggests that the researchers actively implemented or controlled the intervention, which was not the case—the full-day school program was introduced by national education authorities. Since the investigators only observed and compared children naturally enrolled in different schooling models, it would be clearer and more methodologically accurate to describe the groups as “full-day schooling” versus “regular schooling.” This terminology would better reflect the observational nature of the study and prevent readers from misinterpreting it as a researcher-led experiment.

 

Line 110–120 (Materials and Methods): The manuscript presents a conceptual inconsistency in the description of the study design. It is initially defined as “observational,” but later referred to as “quasi-experimental,” and both an “experimental” and a “control” group are described. However, the researchers did not manipulate any independent variable or directly implement the intervention. The Primary School as a Whole-Day School program was a government-led reform, and the investigators simply observed and compared two pre-existing groups: children attending full-day schooling and those in regular schooling.

Although the study includes pre- and post-evaluations, this does not make it experimental, since the defining feature of experimental or quasi-experimental research is the active manipulation of the independent variable by the researchers. In this case, the exposure (schooling type) was determined externally, and the authors only measured outcomes over time. Therefore, the study should be more accurately described as a longitudinal observational design, or alternatively, a natural experiment, given that it evaluates the effects of a naturally occurring policy-driven exposure.

Consistent with this clarification, the groups should not be labeled as “experimental” and “control.” Using more neutral terms such as “full-day schooling” and “regular schooling” groups would better reflect the non-interventional nature of the study and ensure methodological precision.

 

Line 110–121 (Materials and Methods): The manuscript does not specify the sampling strategy (e.g., sampling frame, selection method, inclusion/exclusion criteria, recruitment process, or response rate) used to enroll the 128 participants. Please clarify how participants were selected and allocated to the two schooling models.

 

Line 213–223 (Materials and Methods): There is no a priori sample size calculation or power analysis reported to justify the adequacy of the sample for the mixed-design ANOVA. Please report the planned effect size, alpha, power, and model parameters (or provide a justified alternative such as a post hoc sensitivity analysis).

 

Line 135–140 (Materials and Methods): The manuscript does not clearly define the eligibility criteria for individual participants. While it specifies the age range and grade level of children, it does not indicate how students within each school were selected or whether any exclusion criteria (e.g., health conditions, attendance, consent issues) were applied. Clarifying the inclusion and exclusion criteria at the participant level is essential to ensure transparency and reproducibility, as the current description mainly addresses school-level selection rather than individual eligibility.

Line 140–150 (Materials and Methods):  The manuscript does not include information on ethical approval or informed consent procedures. It should clearly state whether the study protocol was reviewed and approved by an institutional ethics committee, provide the approval code or institution name, and specify how informed consent from parents or guardians and assent from the participating children were obtained. Given that the study involves minors and data collection in schools, the inclusion of these details is essential for compliance with international ethical standards (e.g., Declaration of Helsinki).

 

line 150–160 (Materials and Methods): The manuscript does not specify the setting or conditions under which data collection was conducted. Please indicate where the measurements took place (e.g., within school facilities, laboratories, or another controlled environment), who conducted the assessments, and whether testing conditions (time of day, fasting status, environment) were standardized across both groups. Clarifying these methodological details is crucial to assess data reliability and ensure comparability between the full-day and regular schooling groups.

 

line 125–140 (Materials and Methods): While the manuscript describes general features of the Whole-Day School program (longer school hours, additional PE class, specialized PE teachers, and active breaks), it does not clearly specify the daily activities and actual exposure differences between the full-day and regular schooling groups. Please clarify what each group was exposed to during the school day—particularly the duration, type, and intensity of physical activity opportunities—to better understand how these structural differences might explain the observed outcomes. Providing this information would strengthen the internal validity of the comparison.

 

line 175–210 (Materials and Methods – Variables and Measurements): While the instruments used to assess physical activity and body composition are described in detail, several methodological aspects require clarification. The manuscript does not specify accelerometer wear-time validity criteria, data inclusion thresholds, or cut-points used to classify PA intensity in GGIR. For bioimpedance, assessments were performed after food and fluid intake, which can substantially affect measurement accuracy; fasting or standardized hydration conditions are generally recommended. Furthermore, potential confounding variables (e.g., age, maturation, active commuting, diet) were not controlled, and the text incorrectly refers to PA and body composition as independent variables when they are actually dependent outcomes. 

 

line 213–223 (Statistical Analysis / Results): The statistical analysis represents a strength of the manuscript, as the use of a mixed-design ANOVA is appropriate for the study’s longitudinal comparative approach. However, it is suggested to expand this section by explicitly including the descriptive statistics employed (e.g., mean, standard deviation, confidence intervals) to provide a clearer overview of data distribution and variability. Additionally, it is recommended to report effect sizes—such as partial eta squared (η²p)for the ANOVA and Cohen’s d for post hoc comparisons—to allow readers to assess the magnitude and practical relevance of the observed differences, beyond statistical significance.

 

line 310–360 (Discussion): The discussion section effectively summarizes and interprets the main findings; however, it would benefit from a broader and more critical perspective. Specifically, the authors should compare their results with international evidence from similar whole-school physical activity or extended school day programs, and elaborate on potential behavioral or physiological mechanisms explaining the observed changes. It is also recommended to discuss the study’s methodological limitations—particularly the non-experimental design and lack of confounder control—and to include measures of effect size or references to practical relevance. Expanding these aspects would enhance the scientific depth, external validity, and overall impact of the discussion.

Author Response

REVIEWER 2

Comments and Suggestions for Authors

The manuscript presents an interesting and relevant contribution to the field of school-based physical activity promotion, examining how participation in a Whole-Day School program relates to changes in physical activity and body composition among Croatian children. The topic is timely and aligned with international efforts to evaluate the health impact of educational reforms. The paper is well written, and the use of objective (accelerometry) and subjective (PAQ-C) measures is a methodological strength.

However, several aspects require clarification and improvement to enhance the methodological rigor, transparency, and scientific impact of the study:

 

Line 38–39 (Introduction): Add citations to support the statement “Physical activity (PA) during childhood plays a vital role in supporting healthy growth and development.”

 RESPONSE: Thank you for this helpful suggestion. We have added appropriate citations to support the statement regarding the importance of physical activity for healthy growth and development in childhood., specifically

1. Poitras, V.J.; Gray, C.E.; Borghese, M.M.; Carson, V.; Chaput, J.P.; Janssen, I.; Katzmarzyk, P.T.; Pate, R.R.; Connor Gorber, S.; Kho, M.E.; et al. Systematic review of the relationships between objectively measured physical activity and health indicators in school-aged children and youth. Appl Physiol Nutr Metab 2016, 41, S197-239, doi:10.1139/apnm-2015-0663.
2. Janssen, I.; Leblanc, A.G. Systematic review of the health benefits of physical activity and fitness in school-aged children and youth. Int J Behav Nutr Phys Act 2010, 7, 40, doi:10.1186/1479-5868-7-40.

 

Line 41–42 (Introduction): The phrase “many children worldwide still fall short of the recommended 60 minutes of moderate-to-vigorous PA each day” is too vague. Include specific global or regional data.

 RESPONSE: Thank you for this valuable comment. We agree that the statement was too general. In the revised manuscript, we now include specific global prevalence estimates indicating the proportion of children and adolescents who fail to meet the recommended 60 minutes of MVPA per day, supported by authoritative epidemiological data. Text now reads: “Nevertheless, global surveillance data indicate that approximately 81% of adolescents worldwide do not achieve the recommended 60 minutes of daily MVPA, with insufficient activity consistently observed across regions and income levels [3]“ (please see 1^st paragraph of the Introduction).

 

Line 59–60 (Introduction): Add citations to support the statement “Indeed, PE has been widely recognized as an important setting for increasing children’s PA levels and reducing the risk of being overweight and obesity.”

 RESPONSE: Thank you for this suggestion. We agree that the statement requires supporting evidence. In the revised manuscript, we have added citations from systematic reviews and influential public health literature demonstrating that school-based PE is a key setting for increasing children's PA and can contribute to obesity prevention. Newly added references are:

• Hollis, J.L.; Williams, A.J.; Sutherland, R.; Campbell, E.; Nathan, N.; Wolfenden, L.; Morgan, P.J.; Lubans, D.R.; Wiggers, J. A systematic review and meta-analysis of moderate-to-vigorous physical activity levels in elementary school physical education lessons. Prev Med 2016, 86, 34-54, doi:10.1016/j.ypmed.2015.11.018.
• Kriemler, S.; Meyer, U.; Martin, E.; van Sluijs, E.M.; Andersen, L.B.; Martin, B.W. Effect of school-based interventions on physical activity and fitness in children and adolescents: a review of reviews and systematic update. Br J Sports Med 2011, 45, 923-930, doi:10.1136/bjsports-2011-090186.

 

Line 71–107 (Introduction): This section devotes extensive detail to describing the Croatian educational reform and its administrative structure, which weakens the scientific focus of the introduction. The justification currently rests mainly on the absence of local evidence, but it should also reflect what is already known internationally about the effects of similar whole-day or school-based physical activity programs. Incorporating findings from other countries would strengthen the rationale, demonstrate awareness of the global evidence base, and clarify how this study adds new or complementary knowledge rather than addressing a purely national gap.

 RESPONSE: Thank you for this insightful comment. We agree that the Introduction contained excessive administrative detail about the Croatian educational reform and that this weakened the scientific focus. In the revised manuscript, we have substantially condensed this section and shifted the emphasis toward the international evidence base on whole-day and school-based PA programs. We now highlight findings from comparable interventions in other countries, demonstrating that extended school schedules, increased structured PA opportunities, and PE delivered by specialists can positively influence children’s activity levels and health indicators. This broader context clarifies how our study contributes new evidence by examining the effects of a whole-day school model within the Croatian educational system. Text related to this problem is as follows: “Extended school-day models and whole-school physical activity interventions implemented in several countries have shown that modifying the school schedule to include more structured and unstructured PA opportunities can increase children’s daily activity levels and improve selected health outcomes [11,21]. Programs such as the Finnish ‘Schools on the Move’, and UK active schools have demonstrated that in-tegrating PA throughout the school day, through additional PE lessons, active recess, and extracurricular sport, can contribute to higher MVPA and may support healthy weight trajectories [22,23]. In Croatia, the “Primary School as a Whole-Day School” program follows a similar logic by extending instructional time and embedding more opportunities for movement, including increased PE frequency, specialist-led instruc-tion, and daily recreational breaks.” (please see 5^th paragraph of the Discussion).

 

Line 115–118 (Materials and Methods)
The terminology used to describe the study groups could be misleading. Referring to participants as belonging to an “experimental group” suggests that the researchers actively implemented or controlled the intervention, which was not the case—the full-day school program was introduced by national education authorities. Since the investigators only observed and compared children naturally enrolled in different schooling models, it would be clearer and more methodologically accurate to describe the groups as “full-day schooling” versus “regular schooling.” This terminology would better reflect the observational nature of the study and prevent readers from misinterpreting it as a researcher-led experiment.

 RESPONSE: Thank you for this important clarification. We agree that referring to the groups as “experimental” and “control” may unintentionally imply that the research team implemented or manipulated the intervention. To more accurately reflect the observational design and the fact that the full-day school program was implemented by national authorities, we have revised the terminology throughout the manuscript. The groups are now described as the “full-day schooling group” and the “regular schooling group.” This adjustment improves methodological accuracy and prevents misinterpretation of the study as a controlled experimental intervention.

 

Line 110–120 (Materials and Methods): The manuscript presents a conceptual inconsistency in the description of the study design. It is initially defined as “observational,” but later referred to as “quasi-experimental,” and both an “experimental” and a “control” group are described. However, the researchers did not manipulate any independent variable or directly implement the intervention. The Primary School as a Whole-Day School program was a government-led reform, and the investigators simply observed and compared two pre-existing groups: children attending full-day schooling and those in regular schooling.

Although the study includes pre- and post-evaluations, this does not make it experimental, since the defining feature of experimental or quasi-experimental research is the active manipulation of the independent variable by the researchers. In this case, the exposure (schooling type) was determined externally, and the authors only measured outcomes over time. Therefore, the study should be more accurately described as a longitudinal observational design, or alternatively, a natural experiment, given that it evaluates the effects of a naturally occurring policy-driven exposure.

Consistent with this clarification, the groups should not be labeled as “experimental” and “control.” Using more neutral terms such as “full-day schooling” and “regular schooling” groups would better reflect the non-interventional nature of the study and ensure methodological precision.

RESPONSE: Thank you for this important clarification. We agree that our original wording created conceptual inconsistency by describing the study as both observational and quasi-experimental, and by labeling the groups as “experimental” and “control.” Since the research team did not manipulate the intervention and the schooling model was determined by a government-led reform, the study is more accurately classified. In the revised manuscript, we now refer to the groups as the “full-day schooling group” and “regular schooling group”.

 

Line 110–121 (Materials and Methods): The manuscript does not specify the sampling strategy (e.g., sampling frame, selection method, inclusion/exclusion criteria, recruitment process, or response rate) used to enroll the 128 participants. Please clarify how participants were selected and allocated to the two schooling models.

 RESPONSE: Thank you for the suggestion. It is now specified in more detail in the Methods section.

 

Line 213–223 (Materials and Methods): There is no a priori sample size calculation or power analysis reported to justify the adequacy of the sample for the mixed-design ANOVA. Please report the planned effect size, alpha, power, and model parameters (or provide a justified alternative such as a post hoc sensitivity analysis).

 RESPONSE: Indeed, we couldn’t do the a-priori sample size calculation since we were limited by naturalistic type of experiment (this wasn’t randomized control study). However, in the revised version of the manuscript we provided details on ANOVA effect size as you suggested.

 

Line 135–140 (Materials and Methods): The manuscript does not clearly define the eligibility criteria for individual participants. While it specifies the age range and grade level of children, it does not indicate how students within each school were selected or whether any exclusion criteria (e.g., health conditions, attendance, consent issues) were applied. Clarifying the inclusion and exclusion criteria at the participant level is essential to ensure transparency and reproducibility, as the current description mainly addresses school-level selection rather than individual eligibility.

RESPONSE: Thank you for the suggestion. It is now specified in more detail in the Methods section, and text reads: “All 3rd and 4th graders from selected schools were invited to participate, and parental consent was obtained before the study. The children involved in the study were healthy and regularly participated in the PE classes, while the great majority of them were involved in out-of-school sport programs during the course of this study (74% and 77% of the children in the experimental and control groups, respectively), with no significant difference between the study groups in out-of-school sport involvement. Inclusion criteria included: no health conditions which could prevent children from participating in PE classes, less than 20% of absence from school over the study peri-od, participation in the pre- and post-measurement, parental consent for the partici-pation in the study. Exclusion criteria included health conditions which limited par-ticipation in PE, more than 20% school absences during the study period, non-participation in pre-, or post-testing. Initially, 140 children were tested at pre-testing while post-testing involved 138 children. However, because of the non-meeting inclusion criteria, and necessity of paring pre- and post-testing results, the final sample included altogether 128 children (54 and 74 in experimental, and control group, respectively).”

 

 

Line 140–150 (Materials and Methods):  The manuscript does not include information on ethical approval or informed consent procedures. It should clearly state whether the study protocol was reviewed and approved by an institutional ethics committee, provide the approval code or institution name, and specify how informed consent from parents or guardians and assent from the participating children were obtained. Given that the study involves minors and data collection in schools, the inclusion of these details is essential for compliance with international ethical standards (e.g., Declaration of Helsinki).

 RESPONSE: The ethical approval and informed consent are included at the end of the manuscript, before the References section. Originally, the details on ethical approval were reported at the end of the manuscript, but as you suggested it is now added in the Methods section as well.

line 150–160 (Materials and Methods): The manuscript does not specify the setting or conditions under which data collection was conducted. Please indicate where the measurements took place (e.g., within school facilities, laboratories, or another controlled environment), who conducted the assessments, and whether testing conditions (time of day, fasting status, environment) were standardized across both groups. Clarifying these methodological details is crucial to assess data reliability and ensure comparability between the full-day and regular schooling groups.

 RESPONSE: We added that information in the Variables section, text reads: All measurements for both groups were identical; they took place within school facilities and were conducted by trained kinesiologists. The same measurement protocols, staff, and devices were used at both time points to ensure measurement reliability.

 

line 125–140 (Materials and Methods): While the manuscript describes general features of the Whole-Day School program (longer school hours, additional PE class, specialized PE teachers, and active breaks), it does not clearly specify the daily activities and actual exposure differences between the full-day and regular schooling groups. Please clarify what each group was exposed to during the school day—particularly the duration, type, and intensity of physical activity opportunities—to better understand how these structural differences might explain the observed outcomes. Providing this information would strengthen the internal validity of the comparison.

RESPONSE: Thank you for this suggestion. We now added new table (Table 1) which provides all important detail about the differences between the two programs.   

line 175–210 (Materials and Methods – Variables and Measurements): While the instruments used to assess physical activity and body composition are described in detail, several methodological aspects require clarification. The manuscript does not specify accelerometer wear-time validity criteria, data inclusion thresholds, or cut-points used to classify PA intensity in GGIR. For bioimpedance, assessments were performed after food and fluid intake, which can substantially affect measurement accuracy; fasting or standardized hydration conditions are generally recommended. Furthermore, potential confounding variables (e.g., age, maturation, active commuting, diet) were not controlled, and the text incorrectly refers to PA and body composition as independent variables when they are actually dependent outcomes. 

RESPONSE: The details are now added in the text, please see Variables and Limitations sections. For example, text related to accelerometers now read: “GENEActiv devices record raw triaxial acceleration continuously; therefore, no prede-fined epoch length was applied. Data were processed using the GGIR package, which automatically identifies non-wear periods and applies established GENEActiv-specific thresholds for classifying activity intensities. Participants with detected non-wear time were excluded from the analyses. A minimum of four valid days (≥2 weekdays and ≥2 weekend days) was required for inclusion, consistent with recommended procedures for assessing habitual PA in children. Intensity metrics (LPA, MVPA, VPA) were gen-erated directly by the GGIR algorithm, which calculates activity categories from raw acceleration without requiring user-defined cut-points.”

 

line 213–223 (Statistical Analysis / Results): The statistical analysis represents a strength of the manuscript, as the use of a mixed-design ANOVA is appropriate for the study’s longitudinal comparative approach. However, it is suggested to expand this section by explicitly including the descriptive statistics employed (e.g., mean, standard deviation, confidence intervals) to provide a clearer overview of data distribution and variability. Additionally, it is recommended to report effect sizes—such as partial eta squared (η²p)for the ANOVA and Cohen’s d for post hoc comparisons—to allow readers to assess the magnitude and practical relevance of the observed differences, beyond statistical significance.

 

RESPONSE: Thank you for your suggestion. In this version we included calculation of the effect size (partial et squared), and interpreted it accordingly. The changes are evident in text on statistics, results, Table 2, and later in Discussion.

 

line 310–360 (Discussion): The discussion section effectively summarizes and interprets the main findings; however, it would benefit from a broader and more critical perspective. Specifically, the authors should compare their results with international evidence from similar whole-school physical activity or extended school day programs, and elaborate on potential behavioral or physiological mechanisms explaining the observed changes. It is also recommended to discuss the study’s methodological limitations—particularly the non-experimental design and lack of confounder control—and to include measures of effect size or references to practical relevance. Expanding these aspects would enhance the scientific depth, external validity, and overall impact of the discussion.

RESPONSE: Thank you for this constructive suggestion. We agree that broadening the Discussion by integrating international evidence, elaborating on plausible behavioral and physiological mechanisms, and more explicitly addressing methodological limitations would enhance the scientific depth and interpretability of our findings. In the revised manuscript, we have added comparisons with results from similar whole-school and extended school-day PA programs conducted in other countries.

 

Thank you for your suggestions once again. Staying at your disposal!

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for submitting your manuscript entitled: 
Physical Activity and Body Composition Outcomes of the "Primary School as a Whole-Day School" Program in Early School-Age Children from Croatia.
to Applied Sciences.

Your study presents relevant findings regarding school-based interventions and their impact on children’s physical activity and body composition. The manuscript is well designed, methodologically consistent, and clearly written.

Before publication, however, please consider the following minor revisions:

Complete the Author Contributions section.

Provide the real contact information for the corresponding author.

Improve the figure 1 ( Study design) to describe the intervention process in more detail.

Mention the equipment used for the measurements in the summary. 

Clarify limitations regarding bioimpedance precision and sample size.

Once these points are addressed, the article will be ready for acceptance.

Congratulations on your valuable work and contribution to the field of applied health and education sciences.

Author Response

REVIEWER 3

Comments and Suggestions for Authors

Dear Authors,

Thank you for submitting your manuscript entitled: 
Physical Activity and Body Composition Outcomes of the "Primary School as a Whole-Day School" Program in Early School-Age Children from Croatia.
to Applied Sciences.

Your study presents relevant findings regarding school-based interventions and their impact on children’s physical activity and body composition. The manuscript is well designed, methodologically consistent, and clearly written.

RESPONSE: We thank the reviewer for the positive evaluation of our manuscript and for recognizing the relevance and clarity of our study. We appreciate your constructive feedback, which has helped us further improve the precision, methodological transparency, and overall quality of the manuscript.

 

Before publication, however, please consider the following minor revisions:

 

Complete the Author Contributions section.

RESPONSE: It is now added, thank you.

 

Provide the real contact information for the corresponding author.

RESPONSE: It is now added, thank you.

Improve the figure 1 ( Study design) to describe the intervention process in more detail.

RESPONSE: More details on study are now added in newly added Figure 1, and Table 1 where the flow diagram and differences between observed school programs are specified. Thank you!

 

 

Mention the equipment used for the measurements in the summary. 

RESPONSE: It is now added, thank you.

 

Clarify limitations regarding bioimpedance precision and sample size.

RESPONSE: It is now added in the Methods and Limitations section, thank you.

 

Once these points are addressed, the article will be ready for acceptance.

Congratulations on your valuable work and contribution to the field of applied health and education sciences.

Reviewer 4 Report

Comments and Suggestions for Authors

This study, titled “Physical Activity and Body Composition Outcomes of the ‘Primary School as a Whole-Day School’ Program in Early School-Age Children from Croatia,” evaluates the impact of an experimental full-day school program in Croatia on physical activity and body composition among 9- to 11-year-old children. The research design is well-structured, employing rigorous methods that combine objective and subjective measurement tools, demonstrating both practical and theoretical value. Overall, the article is of high quality and suitable for publication, though minor revisions are recommended to enhance clarity and rigor.

1. Title and Abstract
Title: Clear and concise, accurately reflecting the study content.

Abstract: Structured appropriately, but it is recommended to explicitly state in the results section that “Group E” refers to the experimental group to avoid reader confusion.

2. Introduction
The background is well-established, citing relevant international and domestic data to support the study's necessity.

It is recommended to more explicitly state the research hypothesis at the end of the introduction to align with subsequent sections.

3. Materials and Methods
Study Design: A clearer explanation is needed for choosing a quasi-experimental design over randomized grouping, along with a discussion of potential biases this may introduce.

Sample Description: Recommend adding whether there were significant differences in baseline physical activity and body composition between the two groups of children.

Variable Measurement: Clearly state the duration of accelerometer wear (e.g., whether weekends were included).

Statistical Analysis: Were covariates (e.g., baseline values, participation in extracurricular sports) accounted for in the ANOVA model? Recommend specifying this.

4. Results
Tables 3–5: Clearly define the meaning of the “*” and “Y” symbols in table captions or notes (currently only explained in Table 3).

Gender differences: Results show significant changes in boys' MVPA but not in girls'. Briefly explain possible reasons in the results section to set the stage for discussion.

5. Discussion
The explanation for PA improvement is reasonable, but the claim about “teacher professionalism” influencing PA lacks direct data support. More cautious wording is recommended.

The explanation for no changes in body composition (short duration, no dietary intervention) is reasonable.

The discussion should more explicitly state the practical implications of this study, such as insights for educational policy.

6. Conclusion
The conclusion is concise and consistent with the results.

It is recommended to add “Future studies should focus on long-term effects and the mechanisms underlying gender differences” to the final sentence.

7. Format and Language
Some abbreviations (e.g., Group E) should be spelled out in full upon first use.

The language is generally fluent, but a few sentences are lengthy. It is recommended to break them down appropriately to enhance readability.

Author Response

REVIEWER 4

Comments and Suggestions for Authors

This study, titled “Physical Activity and Body Composition Outcomes of the ‘Primary School as a Whole-Day School’ Program in Early School-Age Children from Croatia,” evaluates the impact of an experimental full-day school program in Croatia on physical activity and body composition among 9- to 11-year-old children. The research design is well-structured, employing rigorous methods that combine objective and subjective measurement tools, demonstrating both practical and theoretical value. Overall, the article is of high quality and suitable for publication, though minor revisions are recommended to enhance clarity and rigor.

1. Title and Abstract
   Title: Clear and concise, accurately reflecting the study content.

Abstract: Structured appropriately, but it is recommended to explicitly state in the results section that “Group E” refers to the experimental group to avoid reader confusion.

RESPONSE: It is now clearly stated, thank you. However, in this version of the manuscript, on the basis of Reviewer suggestion, we used the term “full day school” for experimental, and “regular-schooling” for control group. Thank you.

 

2. Introduction
   The background is well-established, citing relevant international and domestic data to support the study's necessity.

It is recommended to more explicitly state the research hypothesis at the end of the introduction to align with subsequent sections.

RESPONSE: Thank you for this helpful suggestion. We agree that the Introduction would benefit from a more explicit statement of the research hypothesis to ensure stronger alignment with the Methods, Results, and Discussion. In the revised manuscript, we have added a clear hypothesis at the end of the Introduction. It reads: “We hypothesized that the experimental program would result in (i) an increase in PA and (ii) favorable changes in body composition”

 

3. Materials and Methods
   Study Design: A clearer explanation is needed for choosing a quasi-experimental design over randomized grouping, along with a discussion of potential biases this may introduce.

RESPONSE: Thank you for this important comment. We agree that a clearer justification for the chosen study design is needed. In the revised manuscript, we clarify that a randomized design was not feasible because the full-day schooling model was implemented as part of a national educational reform, and schools, not researchers, determined the allocation of students to each curricular model. Consequently, a quasi-experimental (natural experiment) or longitudinal observational approach was the only valid option. We also acknowledge that the lack of randomization may introduce selection and contextual biases, and we have added this as a methodological consideration in the Materials and Methods section.

 

Sample Description: Recommend adding whether there were significant differences in baseline physical activity and body composition between the two groups of children.

RESPONSE: Thank you for this suggestion. We agree that reporting whether baseline differences existed between the two groups strengthens the transparency of the sample description and helps contextualize subsequent analyses. It is included in the Table 1. and 2. Where baseline descriptive statistics (Table 1), and main effect for the factor Group (Table 2) were analyzed.

 

Variable Measurement: Clearly state the duration of accelerometer wear (e.g., whether weekends were included).

RESPONSE: Thank you for highlighting the need for additional methodological detail. In the revised manuscript, we now provide information on wear-time criteria, valid days, and data-processing procedures to improve reproducibility. Regarding epoch length, we did not specify this parameter because GENEActiv devices record raw triaxial acceleration continuously, and the GGIR package extracts activity metrics without the use of predefined epochs. Participants with non-wear periods were excluded from the analyses, and only those with at least four valid days (including a minimum of two weekdays and two weekend days) were retained. Intensity classifications (e.g., LPA, MVPA) were derived directly from the GGIR algorithm, which applies established, device-specific cut-points internally; therefore, manual intensity threshold selection was not required. All of this information has now been added to the Methods section to enhance clarity and comparability.

 

 

Statistical Analysis: Were covariates (e.g., baseline values, participation in extracurricular sports) accounted for in the ANOVA model? Recommend specifying this.

RESPONSE: Thank you for your suggestion. Actually, the basline participation in extracurricular sport is analysed before the ANOVA calculation, and since groups didn’t differ in participation, this variable was not considered as potential covariate. This is stated in Methods section, and text reads: “The children involved in the study were healthy and regularly participated in the PE classes, while the great majority of them were involved in out-of-school sport pro-grams during the course of this study (74% and 77% of the children in the experi-mental and control groups, respectively), with no significant difference between the study groups in out-of-school sport involvement.” (please see Participants section, thank you)

 

4. Results
   Tables 3–5: Clearly define the meaning of the “*” and “Y” symbols in table captions or notes (currently only explained in Table 3).

RESPONSE: The symbols’ definitions are now included in Table legends, thank you.

 

Gender differences: Results show significant changes in boys' MVPA but not in girls'. Briefly explain possible reasons in the results section to set the stage for discussion.

RESPONSE: We believe that adding the effects sizes, and changes done in the Discussion followed your suggestion. Thank you.

 

5. Discussion
   The explanation for PA improvement is reasonable, but the claim about “teacher professionalism” influencing PA lacks direct data support. More cautious wording is recommended.

RESPONSE: Thank you for this observation. We agree that attributing PA improvements directly to “teacher professionalism” may overstate the evidence, as our study did not measure teacher behaviors or instructional quality. In the revised manuscript, we have softened this claim and rephrased it to reflect that specialist-led PE may contribute to higher activity levels based on existing literature.

The explanation for no changes in body composition (short duration, no dietary intervention) is reasonable.

The discussion should more explicitly state the practical implications of this study, such as insights for educational policy.

RESPONSE: Thank you for this helpful suggestion. We agree that explicitly outlining the practical implications will strengthen the relevance of the study for educational policy and school-based PA promotion. In the revised manuscript, we have added a dedicated statement highlighting how the findings can inform decisions regarding PE provision, school scheduling, and the design of whole-day school models.

 

6. Conclusion
   The conclusion is concise and consistent with the results.

It is recommended to add “Future studies should focus on long-term effects and the mechanisms underlying gender differences” to the final sentence.

RESPONSE: Thank you for this helpful suggestion. We agree that explicitly outlining the practical implications will strengthen the relevance of the study for educational policy and school-based PA promotion. In the revised manuscript, we have added a dedicated statement highlighting how the findings can inform decisions regarding PE provision, school scheduling, and the design of whole-day school models.

 

7. Format and Language
   Some abbreviations (e.g., Group E) should be spelled out in full upon first use.

RESPONSE: It is now amended, thank you.

The language is generally fluent, but a few sentences are lengthy. It is recommended to break them down appropriately to enhance readability.

RESPONSE: Thank you for this suggestion we tried to make it more fluent in the revised manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I would like to thank the authors for their detailed and thoughtful responses to my previous comments and for the substantial work invested in revising the manuscript. The paper has clearly improved in terms of methodological transparency, structure, and alignment between the aims, methods, and discussion. The addition of an “Intervention” subsection, the clarification of inclusion/exclusion criteria, the flow diagram, and the expanded description of accelerometer processing and PAQ-C rationale are all valuable enhancements.

Overall, most of my original concerns have been adequately addressed. I consider the manuscript notably clearer and more solid than in the first version. I now have only a few remaining points that I suggest the authors address to further strengthen the paper:

1. Multiple comparisons: consistency between Methods and Limitations

In the revised Statistical Analysis section, the authors now indicate that a Bonferroni correction was applied across tests to control for Type I error inflation. At the same time, the Limitations section mentions the absence of correction for multiple comparisons. These two statements appear inconsistent.

Please clarify this point so that the manuscript is internally coherent. If the Bonferroni correction was applied, the Limitations should be adjusted accordingly (e.g., indicating that the risk of Type I error was reduced but not fully eliminated, given the number of outcomes

2. Interpretation of the STEPS Time × Group × Gender interaction

Thank you for the clarification regarding the STEPS variable. I understand your argument that the significant three-way interaction largely reflects differences between boys and girls rather than a meaningful group- or time-driven effect related to the intervention.

I understand your decision not to discuss STEPS in detail; however, I suggest adding a brief sentence in the Results section to mention that, although a significant Time × Group × Gender interaction was observed for STEPS, it did not reveal a clear intervention-related pattern and was therefore not further interpreted. This would help address potential questions from readers and ensure transparency.

Author Response

REVIEWER 1

I would like to thank the authors for their detailed and thoughtful responses to my previous comments and for the substantial work invested in revising the manuscript. The paper has clearly improved in terms of methodological transparency, structure, and alignment between the aims, methods, and discussion. The addition of an “Intervention” subsection, the clarification of inclusion/exclusion criteria, the flow diagram, and the expanded description of accelerometer processing and PAQ-C rationale are all valuable enhancements.

RESPONSE: Thank you for your support and valuable suggestions!

Overall, most of my original concerns have been adequately addressed. I consider the manuscript notably clearer and more solid than in the first version. I now have only a few remaining points that I suggest the authors address to further strengthen the paper:

1. Multiple comparisons: consistency between Methods and Limitations

In the revised Statistical Analysis section, the authors now indicate that a Bonferroni correction was applied across tests to control for Type I error inflation. At the same time, the Limitations section mentions the absence of correction for multiple comparisons. These two statements appear inconsistent.

Please clarify this point so that the manuscript is internally coherent. If the Bonferroni correction was applied, the Limitations should be adjusted accordingly (e.g., indicating that the risk of Type I error was reduced but not fully eliminated, given the number of outcomes

RESPONSE: Thank you for pointing this out, it is now corrected in the Limitations section, text reads: “Moreover, even though a correction for multiple comparisons was applied, the risk of Type I error was reduced but not fully eliminated, given the number of variables examined. ”

2. Interpretation of the STEPS Time × Group × Gender interaction

Thank you for the clarification regarding the STEPS variable. I understand your argument that the significant three-way interaction largely reflects differences between boys and girls rather than a meaningful group- or time-driven effect related to the intervention.

I understand your decision not to discuss STEPS in detail; however, I suggest adding a brief sentence in the Results section to mention that, although a significant Time × Group × Gender interaction was observed for STEPS, it did not reveal a clear intervention-related pattern and was therefore not further interpreted. This would help address potential questions from readers and ensure transparency.

RESPONSE: Thank you for this comment, it is now added in the Results section to make it more clear, text now reads: “It has to be noted that although a significant Time × Group × Gender interaction was observed for STEPS, it did not reveal a clear intervention-related pattern and was therefore not further interpreted.”

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for your thorough revisions and for addressing the majority of the concerns raised in the previous review. The manuscript has clearly improved in clarity, methodological transparency, and scientific contextualization. The incorporation of international evidence, the expanded methodological descriptions, and the clarification of eligibility criteria and accelerometer procedures are particularly noteworthy.

However, several important issues remain and require further revision before the manuscript can be considered fully aligned with the requested changes:

1. Although the Methods section now correctly describes the study as a natural experiment and uses the terms whole-day schooling group and regular schooling group, the terminology is not consistently applied throughout the manuscript.

• The Abstract still refers to an “experimental program” 

• The Discussion also repeatedly uses the term “experimental program”.

Please ensure that the terminology is harmonized across the entire manuscript and that all references implying researcher-controlled experimentation are removed.

2. Inconsistency in reporting multiple-comparison procedures. There is a contradiction between:

• Statistical Analysis section, which states that a Bonferroni correction was applied, and

• Limitations section, which states that no correction for multiple comparisons was applied.

Author Response

REVIEWER 2

Thank you for your thorough revisions and for addressing the majority of the concerns raised in the previous review. The manuscript has clearly improved in clarity, methodological transparency, and scientific contextualization. The incorporation of international evidence, the expanded methodological descriptions, and the clarification of eligibility criteria and accelerometer procedures are particularly noteworthy.

However, several important issues remain and require further revision before the manuscript can be considered fully aligned with the requested changes:

1. Although the Methods section now correctly describes the study as a natural experimentand uses the terms whole-day schooling groupand regular schooling group, the terminology is not consistently applied throughout the manuscript.

The Abstract still refers to an “experimental program” 

The Discussion also repeatedly uses the term “experimental program”.

Please ensure that the terminology is harmonized across the entire manuscript and that all references implying researcher-controlled experimentation are removed.

RESPONSE: Thank you for this comment. We agree that the terminology must be fully consistent across the manuscript. In the revised version, we ensured that all terms implying a researcher-controlled experiment were removed.

At the same time, the phrase “experimental program” is the official terminology used by the Ministry of Science and Education to describe the national pilot implementation of the whole-day school model. Therefore, we are using term “national experimental schooling program” to make it more clear.

2. Inconsistency in reporting multiple-comparison procedures. There is a contradiction between:

Statistical Analysis section, which states that a Bonferroni correction was applied, and Limitations section, which states that no correction for multiple comparisons was applied.

RESPONSE: Thank you for pointing this out; it is now corrected in the Limitations section, text reads: “Moreover, even though a correction for multiple comparisons was applied, the risk of Type I error was reduced but not fully eliminated, given the number of variables examined. ”