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Article

Effects of Increased Letter Spacing on Digital Text Reading Comprehension, Calibration, and Preferences in Young Readers

by
Shahar Dotan
* and
Tami Katzir
Edmond J. Safra Brain Research Center for the Study of Learning Disabilities, Department of Learning Disabilities, University of Haifa, Haifa 3498838, Israel
*
Author to whom correspondence should be addressed.
Educ. Sci. 2025, 15(10), 1306; https://doi.org/10.3390/educsci15101306
Submission received: 17 July 2025 / Revised: 6 September 2025 / Accepted: 26 September 2025 / Published: 2 October 2025
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Abstract

In educational technology environments, the ability to customize digital text presentation offers opportunities to enhance learning experiences through typographical adjustments. This study investigated how digital letter spacing (LS) manipulations affect reading comprehension (RC), reading speed, calibration of comprehension (CoC), and preferences in emergent readers. We examined 163 second graders and 126 third graders as they read digital texts in Hebrew under two conditions: standard LS (100%) and increased LS (150%). The results revealed developmental differences in response to spacing manipulations: increased LS significantly improved RC in second graders, whereas it showed an opposite trend for third graders. Reading rate remained stable across conditions for both groups. Children also demonstrated more accurate CoC under their individually optimal LS condition, suggesting that their comprehension monitoring was responsive to typographical features that supported reading. Preferences analysis indicated a higher numerical proportion of participants favoring the standard LS condition over the increased LS condition in both grades. These findings imply that by integrating adaptive typographical features into educational technology, educators can enhance performance in developing readers, supporting differentiated instruction in increasingly digital learning environments.

1. Introduction

The pervasive integration of technology in educational contexts has transformed instructional approaches, particularly in literacy development. As schools increasingly adopt digital learning platforms, it becomes essential to examine how text presentation influences cognitive processing and learning outcomes (Moreno & Mayer, 1999; Mayer & Moreno, 2003). Digital environments offer opportunities to personalize learning through adjustable typographical features, which may help address individual differences in visual processing and reading development. Text legibility, the ease with which the visual system processes written information, represents a foundational component of reading that can significantly impact cognitive load and learning efficiency. Optimizing legibility can reduce extraneous processing demands, allowing learners to allocate greater cognitive resources to comprehension rather than decoding (Sweller, 1994; Paas et al., 2004). This cognitive load reduction is particularly important for developing readers who have not yet automatized basic reading processes (Katzir et al., 2013).
A growing body of research shows that typographical properties, including font size, font type, line length, and spacing, affect legibility and reading outcomes (Lonsdale et al., 2006; Woods et al., 2005; Bernard et al., 2002; Chan & Lee, 2005; Schneps et al., 2013). Nonetheless, instructional materials designs have not been empirically validated across diverse learner populations (Montani et al., 2014). This limitation highlights the need to develop evidence-based design principles for educational content.
The versatility of digital text displays creates opportunities to design materials that support different stages in reading development. Yet, research on how children interact with digital text, particularly concerning the relationship between typographical design and their reading, remains limited. The present study addresses this gap by investigating how a letter spacing (LS) manipulation in digital text in Hebrew influences reading comprehension (RC), comprehension monitoring, and children’s display preferences during the critical transition from second to third grade.

1.1. Integrating Visual Processing and Cognitive Load in Reading Development

According to the Simple View of Reading (SVR; Gough & Tunmer, 1986), RC is the product of decoding and language comprehension. More complex models, such as the Lexical Quality Hypothesis (Perfetti, 2007) and the Component Model of Reading (Joshi & Aaron, 2000) highlight additional influences, including vocabulary quality, orthographic knowledge, and inference processes. Decades of research across multiple languages have supported and refined these frameworks, demonstrating that the relative contributions of these components shift with development (Hoover & Gough, 1990; Florit & Cain, 2011). Empirical studies consistently show that for beginning readers, decoding is a significant and resource-demanding component of comprehension. In later grades, as decoding becomes more automatized, higher-level linguistic and cognitive skills play a larger role (Ehri, 2005; Bar-On, 2011). For developing readers in the early grades, decoding is not yet fully automatized and therefore is effortful and resource-intensive. In second grade, children are still mastering grapheme–phoneme mapping and often engage in laborious, letter-by-letter and word-by-word reading. This places high demands on working memory and reduces the capacity available for meaning construction (LaBerge & Samuels, 1974; Perfetti, 1985). By third grade, however, many children have become noticeably more fluent, with greater automaticity in word recognition (Bar-On, 2011; Ehri, 2005; Schwanenflugel et al., 2006). This developmental shift reduces the attentional resources required for decoding, enabling children to allocate more capacity to higher-level comprehension processes and monitoring their understanding (Yeomans-Maldonado, 2017).
The Cognitive load theory emphasizes that working memory has a limited capacity and that excessive demands on this capacity can hinder learning (Sweller, 1994). From this perspective, in reading, typographical features that facilitate grapheme recognition and reduce visual processing demands can free cognitive resources for comprehension processes. Moreno and Mayer (1999) demonstrated that optimizing presentation formats can reduce cognitive load and improve learning outcomes in multimedia environments, a principle that may extend to text presentation (e.g., Dotan & Katzir, 2018; Zorzi et al., 2012). These insights align with capacity theories of attention (Kahneman, 1973) and cognitive processing, which suggest that reducing demands in lower-level processes can enhance performance in higher-level tasks. Additionally, information processing models of reading (Adams, 1990) highlight the importance of efficient visual processing as a foundation for reading. In this context, it is essential to distinguish between reading speed and comprehension, as faster word recognition does not automatically translate into improved understanding of text. Comprehension depends on higher-level cognitive processes that go beyond visual efficiency (Joshi & Aaron, 2000; Perfetti, 2007). For example, Ginestet et al. (2019) modeled the length effect in lexical decision tasks and showed that visual attention can increase reading speed without directly enhancing comprehension. Mayer and Moreno (2003) proposed that reducing extraneous processing demands, such as those imposed by suboptimal text presentation, allows learners to allocate more cognitive resources to essential processing required for comprehension. Thus, typographical manipulations such as increased LS may reduce visual processing demands and cognitive load, thereby enabling greater allocation of resources to comprehension as children transition from effortful decoding to greater fluency.

The Case of Hebrew Reading Development

The current study focuses on Hebrew second- and third-graders. Reading development in Hebrew illustrates both universal and language-specific processes and provides an important context for evaluating typographical manipulations. Hebrew is a Semitic language written in an abjad, a consonantal writing system in which vowels are either omitted or given secondary status. It has two orthographic versions: a fully vowelized pointed script, typically used during the early stages of reading instruction, and an unpointed script, which becomes the default for skilled readers (Bar-On, 2011; Shany & Share, 2011; Shechter & Share, 2025). The transition to unpointed script, usually around Grade 3, requires children to rely more heavily on morphological and morpho-syntactic cues to disambiguate homographs and decode unfamiliar words (Bar-On, 2011; Share, 1999, 2004). At this stage, children are also assumed to shift toward more holistic word recognition, processing words as whole units rather than letter by letter.
This trajectory differs from that observed in English and other alphabetic languages. Whereas readers of English often continue to struggle with accuracy due to irregular grapheme–phoneme correspondences, Hebrew readers typically achieve accuracy early but continue to face challenges in developing fluency and efficiency in the unpointed script (Shany & Share, 2011; Share et al., 2019). Moreover, the root-and-pattern morphology of Hebrew places exceptional demands on morphological awareness as a foundation for fluent reading (Share, 1999, 2004; Share et al., 2019).
These distinctive characteristics raise the possibility that typographical manipulations, such as adjustments in LS, may interact differently with Hebrew’s morpho-orthographic system than with alphabetic systems like English, Italic or Spanish. The present study, therefore, contributes to a broader understanding of how script-specific features may moderate the impact of visual text presentation on reading development.

1.2. LS and Visual Crowding: Developmental Perspectives

The potential benefits of increased LS are grounded in the visual crowding effect (Bouma & Legein, 1977; Martelli et al., 2009; Spinelli et al., 2002), a perceptual phenomenon whereby target identification becomes more difficult when surrounded by other objects. In this case, the targets’ identification becomes more challenging compared to when it is presented in isolation (Pelli et al., 2007; Pelli, 2008; Whitney & Levi, 2011). Object identification typically begins with feature detection and then progresses to feature integration. In crowding, the target object is detected, but its identification is hindered because it appears jumbled with its neighboring objects (Pelli et al., 2004). Developmental research indicates that crowding effects are more pronounced in younger children and diminish with age, typically normalizing around age nine (Bondarko & Semenov, 2005; Jeon et al., 2010; Semenov et al., 2000). It was suggested that the reason that crowding interferes more strongly with children is that their visual system integrates features over larger spatial regions due to immaturities in the retina and higher cortical areas (V2–V4). With age, as retinal sampling, cortical pruning, and inhibitory mechanisms mature, critical spacing between objects shrinks, making recognition more efficient and reducing the crowding effect by about age 9 (Jeon et al., 2010; Semenov et al., 2000). This developmental trajectory suggests that typographical interventions targeting crowding effects may be particularly beneficial for younger readers who have not yet developed adult-like visual processing capabilities.
Various studies have revealed that crowding plays a role in recognizing diverse objects, from simple elements as bars to more intricate ones like letters, words, and faces (Pelli, 2008; Pelli & Tillman, 2008; Whitney & Levi, 2011). Parkes et al. (2001) demonstrated that crowding has a more significant impact when the target object is similar to the distractors, such as in the case of letters.
The Visual Crowding Effect in Reading (Bouma & Legein, 1977; Martelli et al., 2009; Perea et al., 2012; Spinelli et al., 2002) implies that identifying a specific letter becomes more challenging when other letters are positioned closely nearby (Bouma, 1970; Perea et al., 2012). Hence, during reading, crowding interferes with integrating sequential letters into words, leading to difficulties in recognizing the words (Bouma, 1973; Bouma & Legein, 1977; Martelli et al., 2009; Spinelli et al., 2002). Moreover, crowding may not only affect individual letters but also words within sentences (Chung, 2004).
It was suggested that in crowding, the identification of target objects is impaired when the neighboring distractors are closer than a critical spacing (e.g., Martelli et al., 2009; Yu et al., 2007). Indeed, the crowding of letters within a word was shown to be reduced by text display manipulations involving enlarging the LS (Legge & Bigelow, 2011; Pelli et al., 2004; Pelli et al., 2007).
Most research on the effect of LS on reading has focused on struggling readers (Arditi et al., 1990; Gori & Facoetti, 2015; Marinus et al., 2016), whereas fewer studies have examined its effects among typically developing young readers (for a summary of the studies on LS and reading, see Supplementary Materials). Studies focusing on the effect of manipulating LS on single-word reading reveal mixed results. Dotan and Katzir (2018) have found that increased LS improves first-graders’ and low-achieving third-graders’ oral reading accuracy of isolated words. No effect was found on the oral reading speed. In contrast, using a lexical decision task, Perea et al. (2012) found that typical and dyslexic second and fourth-grade readers read faster in increased LS conditions, with no effect found on decision accuracy. van den Boer and Hakvoort (2015) found that second and fourth-graders show reduced reading speed and accuracy when LS is smaller than the default (i.e., in an increased crowding condition) (see similar results in Montani et al., 2014), yet the optimal LS for second and fourth graders was standard, rather than increased.
While single-word reading requires fewer saccades and is less influenced by peripheral visual information, sentence and text reading demand a higher level of visual and cognitive processing. As a result, LS manipulations at the sentence or text level may produce varying effects on reading accuracy and speed. Hughes and Wilkins (2002) found that typically developing 6–11-year-old children in England read sentences more accurately and quickly in increased LS conditions, especially in second grade. It is important to note that their study used A3-sized text at a 4.57-m viewing distance, an arrangement that does not reflect typical reading conditions, such as a computer screen, book, or standard paper. Similarly, Hakvoort et al. (2017) observed improved reading accuracy (but not speed) among both typical and dyslexic third- and fourth-grade readers in increased LS conditions. However, other studies have reported no significant improvements in reading accuracy or speed for typically developing readers in third grade and above when reading sentences or whole texts with increased LS (e.g., Perea et al., 2012; Zorzi et al., 2012).
Only a few studies have investigated the influence of increased LS on RC, and even fewer have focused on children. Schneps et al. (2013) showed that struggling high school readers recalled the content of the passage they read more accurately when presented with increased LS. Perea et al. (2012) indicated that fourth-grade dyslexic readers achieved higher comprehension accuracy in the increased spacing condition compared to standard spacing, but this effect was not observed in normally developing fourth graders (Experiment 4).
To conclude, evidence suggests that the benefits of LS for RC in typically developing children diminish by fourth grade (around age 10), when visual crowding is no longer a major constraint. In contrast, studies with younger readers have reported positive effects of increased LS on oral reading performance. Much of this research, however, has centered on word-level accuracy and speed, often in struggling readers, with mixed findings for typically developing children. Far fewer studies have examined the effects of LS on text-level comprehension, particularly in the early elementary years. This developmental transition from Grade 2 to Grade 3 is especially critical, as decoding becomes increasingly automatized and cognitive resources can be reallocated to comprehension. To date, only one study has investigated Hebrew readers specifically (Dotan & Katzir, 2018). The present study therefore addresses these gaps by examining the impact of LS on RC in typically developing Hebrew second- and third-grade readers in digital text environments.

Comprehension Monitoring in Early Reading: Reader, Task, and Text Influences

Research indicates that effective learning depends on the learner’s ability to evaluate their acquired knowledge and monitor their comprehension (Gutierrez & Schraw, 2015; Temelman-Yogev et al., 2024; Thiede et al., 2003). Comprehension monitoring is the readers’ ability to be aware of their level of understanding of the text and their learning processes (Maki & Berry, 1984; Zhang & Zhang, 2019). After reading a text and answering comprehension questions, readers assess their knowledge level and decide whether to reread parts of the text to answer the questions optimally (Rawson et al., 2000; Temelman-Yogev et al., 2020). Students who succeed in this learning regulation task achieve better results (Dunlosky et al., 2005; Grabe, 2014; Thiede et al., 2003). Children’s comprehension monitoring ability is operationally examined in terms of Calibration of Comprehension (CoC) (Glenberg & Epstein, 1985; Temelman-Yogev et al., 2024). The concept of CoC captures the correspondence between actual comprehension performance (e.g., percentage of correctly answered questions) and readers’ confidence in their performance (e.g., percentage of items judged correct) (Pallier et al., 2002; Schraw, 2009; Thiede et al., 2009).
Multiple factors contribute to individual differences in CoC. At the reader level, comprehension skill is strongly associated with calibration accuracy. Empirical studies consistently show that weaker comprehenders tend to overestimate their performance. For example, less skilled 10-year-olds demonstrated poorer monitoring when processing anaphoric devices compared to skilled peers (Ehrlich et al., 1999). Similar patterns have been documented in adolescents, with good comprehenders showing more accurate calibration than poor comprehenders (Kleider-Tesler et al., 2019), and in adults, where lower verbal ability predicted greater overconfidence in comprehension judgments (Maki et al., 2005). Moreover, the development of CoC parallels broader patterns of cognitive growth. Evidence indicates that metacognitive skills gradually mature during the elementary school years, with monitoring and evaluation processes typically emerging around ages 8–10 and becoming progressively more sophisticated throughout schooling (Veenman et al., 2006). Younger readers often display inflated confidence and overestimation of their comprehension, whereas older readers demonstrate progressively greater accuracy in judging their understanding. However, longitudinal evidence indicates that growth in comprehension monitoring is most pronounced between Grades 1 and 2, followed by a deceleration in later grades (Yeomans-Maldonado, 2017). Similarly, Cain et al. (2004) found that monitoring skill accounted for unique variance in comprehension among 7–11-year-olds, and Helder et al. (2016) observed developmental gains in error detection from ages 8 to 11.
Importantly, these skills are not only shaped by age and reading level but also by contextual factors, such as text presentation. For example, Dinsmore and Parkinson (2013) demonstrated that confidence judgments are influenced not only by personal factors, but also by task characteristics. One factor shown to shape comprehension monitoring is the level of text difficulty. Research indicates that monitoring accuracy is highest when readers engage with texts of intermediate difficulty, compared to texts that are either too simple or excessively challenging (Bjork, 1994; Bjork & Bjork, 2020; Maki et al., 1990; Weaver & Bryant, 1995). According to the optimum effort hypothesis (Weaver & Bryant, 1995), very easy texts require minimal cognitive resources, encouraging an “automatic reading mode” in which monitoring is underutilized. Conversely, very difficult texts demand so much cognitive effort that insufficient capacity remains for monitoring. By contrast, texts of moderate difficulty promote a more balanced allocation of resources, enabling more accurate monitoring of comprehension.
In this context, text display manipulations can be viewed as external features that alter the difficulty of a text, thereby shaping calibration in interaction with the reader’s ability. For example, Dahan-Golan et al. (2018) found that fifth- and sixth-grade students demonstrated more accurate calibration and higher RC in print than on screen, suggesting that children are often better calibrated when texts are presented in a format that optimizes their performance. However, only limited research has examined the relation between CoC and typographical features of text. Studies on font size indicate effects on word memory and metacognitive judgments (Chang & Brainerd, 2022; Halamish et al., 2018; Luna & Albuquerque, 2022), yet the specific impact of LS on comprehension monitoring and calibration has not been systematically investigated, particularly in developing readers. Consequently, typographical features such as LS may influence the cues readers draw upon to evaluate their comprehension, thereby affecting CoC as well as comprehension outcomes.

1.3. Display Preferences and Performance

Few studies have addressed preferences of text display characteristics from the reader’s perspective and their relationship to reading performance (Chan & Lee, 2005). Related terms, such as the perception of “reading ease” were found to be unrelated to objective reading performance (Dyson & Kipping, 1998). In their study, Dyson and Kipping (1998) indicated that the level of ease ratings of different line length displays did not correlate with actual reading performance under these conditions. A sense of familiarity with different text characteristics can also lead to certain preferences (Luna et al., 2023). Furthermore, the motivation to read a text presented in a specific manner (e.g., digital text with interactive features like games, hotspots, etc.) might be higher and could manifest as preferences for such presentations, even though they may hinder text comprehension (Hoffman & Paciga, 2014; Parish-Morris et al., 2013; Takacs et al., 2015). Hence, such results may indicate that preferences are shaped more by the reader’s comfort, familiarity, and motivation, rather than by objective performance, highlighting the central role of subjective experience in reading choices.
Most of the research that focused on reading-related preferences comes from studies on preferred modalities (e.g., Dotan & Katzir, 2024; Eutsler & Trotter, 2020; Huang et al., 2012). These findings reflect children’s suboptimal choices when choosing a medium for their reading assignments. For instance, Dahan-Golan et al. (2018) showed that fifth and sixth graders understood text better when reading on paper compared to screens, even though most children preferred screen reading (see also Jamali et al., 2009; Stone & Baker-Eveleth, 2013; Singer & Alexander, 2017). Interestingly, this study also suggested that children’s preferences for computers tended to decrease after performing tasks under the two modalities, which may reflect children’s awareness of their optimal performance after task completion.
Few studies have examined preferences related to typographical characteristics of text. A study concerning adult preferences, incorporating factors like LS, font size, and background color, indicated a preference for default LS over increased LS (Grobelny & Michalski, 2015). In children, empirical evidence from Hughes and Wilkins (2002) has demonstrated that children prefer larger font sizes and increased LS over default spacing. These children also named the increased LS text as the easiest-to-read text.
Overall, research indicates that readers’ display preferences are driven more by familiarity, comfort, and motivation than by objective performance. However, limited research has examined such preferences in developing readers. The present study addresses this gap by investigating LS preferences among second and third-grade children and their correspondence with reading performance.

1.4. The Current Study

This study examines the effects of LS manipulations on RC, reading speed, CoC, and display preferences among second- and third-grade Hebrew readers. We address three research questions:
  • How does increased LS affect RC and reading speed across developmental stages? We hypothesize that increased LS will enhance comprehension for second graders but not for third graders, reflecting developmental shifts in visual processing and reading strategies, while no effect is expected on reading speed (Dotan & Katzir, 2018; Ginestet et al., 2019; Hughes & Wilkins, 2002).
  • How does LS affect children’s CoC? We hypothesize that children will demonstrate more accurate CoC under conditions that optimize their RC (Dahan-Golan et al., 2018), reflecting the development of comprehension monitoring at a young age (Yeomans-Maldonado, 2017).
  • How does LS affect children’s display preferences before and after reading tasks? We hypothesize that children will initially prefer standard LS due to familiarity, with preferences potentially shifting after experiencing both conditions (Dahan-Golan et al., 2018).

2. Method

2.1. Participants

The study included a total of 289 participants, comprising 163 s graders (89 female) and 126 third graders (61 female), selected from 8 elementary schools in Israel. All participants had normal or corrected to normal vision and hearing. The experiment was conducted at the end of the 2021 academic year.

2.2. Procedure and Materials

This study received approval from the Israeli Ministry of Education (protocol number 10664/19) and the Ethics Institutional Review Board at the authors’ institution. It was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. Informed parental consent forms were sent to parents before the commencement of the study. The children provided their oral participation consent and were informed of their ability to discontinue their participation at any time during the experiment. Due to COVID-19 restrictions preventing research assistants from entering the school, teachers received training to deliver research assignments. Importantly, the teachers were unaware of the research questions or hypotheses. The supervision of assignment transfer was carried out by the research team.

2.3. RC Task

The RC task involved two texts for each grade: “I Need to Do Something” and “My sister has a High Fever” for second grade (Katzir et al., 2013), and “The Zebra and the Pajamas” and “My Pet Snake” for third grade (Sabag-Shushan & Katzir, 2024). The short texts contained 45 words for second grade and 70–74 words for third grade, followed by four multiple-choice comprehension questions for second grade and five for third grade. The tools’ reliability, as indicated by Cronbach’s α for a pilot sample before running the main experiment, ranged from 0.70 to 0.86 (see also reliability of these texts in Katzir et al., 2013—0.756, and Sabag-Shushan & Katzir, 2024—0.69–0.86).
Participants sat in a school computer classroom, in front of a 21-inch computer screen. Texts were presented in the “Narkisim” font type, representing the font and text dimensions used in nationwide printed textbooks and their digital version (“Mila Tova”) for reading acquisition. The font size was 16 pt (0.56 cm), reflecting the typical digital font size required by these grades. Based on the Angular size equation (Angular size = 5.73 × physical size/viewing distance), and the optimal angular size for maximum reading speed (0.2–2°) (Legge & Bigelow, 2011; Legge et al., 1985; Pelli et al., 2007), the viewing distance for all readers was 40 cm from the screen (reflecting an angular size of 0.8°).
Participants completed the two-text RC task at their own pace. The texts were divided into two phases representing two spacing conditions: the increased LS phase and the standard LS phase. The standard LS (100%) condition reflected the typical LS used in textbooks of these grades. In the increased LS condition, the text presentation had the spacing between letters increased to 150% (based on Dotan & Katzir, 2018). In this condition, the spacing between words was increased proportionally. The two LS conditions were presented sequentially, and their order was counterbalanced between participants, with half starting with the standard LS condition and the other half beginning with the increased LS condition. A two-minute break between phases was implemented to avoid display-shifting effects on performance. Figure 1 illustrates the two LS conditions.
Two measures were derived from this task: the RC accuracy percentage, and the reading speed which was recorded from the moment the text appeared on the screen to the point when readers pressed the ‘next’ button.
In order to address the second research question focused on whether CoC of children is dependent on their optimal LS display for performance, we calculated the optimal spacing for each participant by subtracting their RC score in the increased LS condition (Increased RC) from the score in the standard LS condition (Standard RC), following the method outlined in Halamish and Elbaz (2020). Participants who achieved a positive score were grouped into the first category: the ‘Optimal Standard Spacing’ group (OSS group). Those who received a negative score fell into the second category: the ‘Optimal Increased Spacing’ group (OIS group). Participants with a score of zero were categorized into the third group: ‘Equivalent performance’ (EP group).

2.4. CoC Ratings

After answering the comprehension questions, the participants were asked how many questions they believed they had answered correctly. This number reflected the children’s confidence ratings in their answers. Then, the confidence in answering the questions was rated on a percentage scale (0%—no confidence; 100%—complete confidence). To calculate the CoC measure, the RC accuracy percentage was subtracted from the confidence rating percentage. The CoC measure was calculated for each of the LS conditions (standard and increased LS). A positive CoC value indicated that children overestimated their performance, a negative value indicated that children underestimated their performance, and a value of zero indicated a perfect estimation of performance.

2.5. Preference Questions

Each of the participants also answered a preference question prior to and after the experiment, concerning their preferred LS display. The two LS conditions were presented to the children, and they had to choose their preferred display: (1) Standard LS (100%); (2) Increased LS (150%), or (3) No preference. These questions were developed based on a study on medium reading preferences (Dahan-Golan et al., 2018).
The anonymized data and analysis scripts supporting this study are openly available in a dedicated online repository. This study was not preregistered.

3. Results

3.1. The Effect of LS on Reading Performance

To answer the first research question regarding the differences in RC and reading speed between the two spacing conditions in the second and third grades, univariate analyses of variance (ANOVAs) were run separately for the second grade and third grade.

3.2. The Effect of LS RC

As expected, in the second grade, increased LS yielded a significantly higher RC (M = 0.72, Sd = 0.29) than the standard LS condition (M = 0.67, Sd = 0.28), F (1, 162) = 4.57, p < 0.05, η2 = 0.03. In the third grade, results indicated an approaching significance opposite trend, with higher comprehension in the standard LS condition (M = 0.71, Sd = 0.26), compared to the increased LS condition (M = 0.66, Sd = 0.26), F (1, 125) = 3.37, p = 0.07, η2 = 0.03. Figure 2 presents the differences in RC between the two LS conditions in the second and third grades.

3.3. The Effect of LS on Reading Speed

The analyses of the effect of increased LS on speed supported our expectations. No differences were observed between the two spacing conditions, neither for the second grade, F < 1 (Standard LS: M = 101.84, Sd = 58.82, Increased LS: M = 105.93, Sd = 64.34), nor for the third grade, F < 1 (Standard LS: M = 83.52, Sd = 48.75, Increased LS: M = 87.44, Sd = 48.16).

3.4. The Effect of LS on CoC

In order to run the main analysis to answer the second research question regarding the correspondence between CoC and children’s optimal LS, we first analyzed children’s optimal LS. Descriptive statistics of the optimal display subgroups are presented in Table 1. As shown in Table 1, 41% (n = 67) of second graders performed optimally in the increased LS condition (OIS group), 24% (n = 39) in the standard LS condition (OSS group), and 35% (n = 57) performed equally in both conditions (EP group). Among third graders, 44% (n = 55) performed optimally in the standard LS condition (OSS group), 26% (n = 33) in the increased LS condition (OIS group), and 30% (n = 38) performed equally in both conditions (EP group). These distributions align with the reading comprehension results reported in the previous section, supporting Hypothesis 1.
The next step of analysis focused on examining whether the CoC of children is dependent on their optimal LS display for performance. Separate t-tests on CoC were performed for the three groups in both grades. The analyses in the second and third grades confirmed our expectations. The OSS group was significantly more calibrated in the standard LS than the increased LS [t(34) = 5.86, p < 0.001, Cohen’s d = 0.32 for second grade; t(50) = 8.42, p < 0.001, Cohen’s d = 0.28 for third grade]. The OIS group showed an opposite significant trend, by which CoC was more accurate on the increased LS condition, compared to the standard LS condition [t(64) = 6.56, p < 0.001, Cohen’s d = 0.26 for second grade; t(29) = 8.60, p < 0.001, Cohen’s d = 0.22 for third grade]. There was no effect of spacing on the EP group, indicating similar CoC in both conditions. Descriptive statistics and t-values are presented in Table 2 and Figure 3.

3.5. LS and Preferences

To address the third research question regarding the effect of LS on readers’ preferences, we analyzed preference ratings before and after the RC tasks. The results of the pre-task analysis supported our hypothesis, showing a higher proportion of participants who favored the standard LS condition over the increased LS condition, both in Grade 2 (47% vs. 34%) and in Grade 3 (42% vs. 32%).
After completing the RC task, the distribution of preferences became more balanced, yet the standard LS condition continued to be favored to a greater extent (41% compared to 30% in the second grade, and 39% compared to 31% in the third grade). Figure 4 presents the proportions of preferences among participants in the second and third grades.
Further, we examined whether there is a relation between the optimal LS display for RC of the reader and his preferences. Chi-squared analyses between preference (increased LS, standard LS, no preference) and optimal display group (OIS, OSS, EP) were performed to investigate whether children did, in fact, prefer the optimal LS presentation for their RC performance. As indicated in Table 3, chi-square correlations between preference and actual performance group among both second and third-grades were not statistically significant, suggesting that participants did not choose their optimal display condition. In addition, a further chi-squared analysis was run to examine the stability of preferences before and after performing the reading task. Results showed that the relation between children’s pre- and post-task preferences was significant, implying that these participants demonstrated consistency in their preferences. Table 3 presents the chi-squared values.

4. Discussion

This study explored the effects of increased LS on RC, reading speed, CoC, and display preferences among second and third-grade Hebrew developing readers. The findings offer insights into understanding how typographical manipulations may be related to these aspects in early readers, with important implications for the design and implementation of educational technologies.

4.1. Developmental Trajectory of LS Effects

The first part of our study demonstrated that increased LS was positively related to RC for second graders, while this positive trend disappeared, and even showed an opposite trend, in third graders. These findings align with developmental theories of visual processing and reading acquisition, suggesting that the crowding effect is particularly influential in the early stages of reading development and gradually diminishes with age (Bondarko & Semenov, 2005; Jeon et al., 2010; Semenov et al., 2000). This developmental shift typically occurs around age 9. In the Israeli school system, children are generally 7–8 years old in Grade 2 and 8–9 years old in Grade 3. Because the present data were collected at the end of the school year, it is likely that most third-grade participants were already age 9. This timing corresponds with our observed grade-level differences and is consistent with the interpretation that the reduced facilitative effect of increased LS in Grade 3 may be associated with a developmental decrease in crowding interference.
The contrasting patterns observed between second and third graders can be interpreted through information-processing models of reading (Adams, 1990) and developmental theories (Bar-On, 2011). Early readers rely on serial letter-by-letter decoding, which is particularly susceptible to visual crowding. Increasing LS may reduce this interference, facilitating grapheme identification and freeing cognitive resources for comprehension, consistent with cognitive load theory (Sweller, 1994; Paas et al., 2004). By third grade, however, children begin transitioning to holistic word recognition (Aghababian & Nazir, 2000; Bar-On, 2011; Share, 1999, 2004). In this stage, wider spacing can fragment words and extend them into peripheral vision, potentially disrupting rather than supporting fluent processing (Bosse & Valdois, 2009; Bouma & Legein, 1977). In Hebrew specifically, this shift to whole-word recognition may explain why spacing manipulations become less beneficial, aligning with Dotan and Katzir’s (2018) finding that spacing primarily supports longer words, where crowding effects are more pronounced.
Our finding that reading speed remained unaffected by LS manipulations across both grade levels. As Ginestet et al. (2019) showed, faster reading does not necessarily translate into improved comprehension, and reading comprehension gains may occur without corresponding increases in speed. These fundings contribute to the complex picture emerging from prior research. While Perea et al. (2012) observed a faster reading speed in lexical decision tasks with increased LS, our results align with Dotan and Katzir’s (2018) findings, where reading speed remained unchanged for isolated words. Other studies have shown varying effects of LS on reading speed, with inhibitory effects in longer sentences and paragraphs (Yu et al., 2007; Schneps et al., 2013), and facilitative effects in single words and short sentences (Perea & Gomez, 2012a, 2012b; Perea et al., 2011; Spinelli et al., 2002; Zorzi et al., 2012), see Supplementary Materials. These contrasting findings may stem from differences in study methodologies. Future studies investigating LS effects on reading should compare oral to silent continuous reading tasks, which could provide a more accurate understanding of the effect of LS on reading speed.

Comprehension Monitoring and Text Typography

Another notable finding concerns the relationship between LS and CoC. Children showed more accurate calibration of comprehension when reading under the LS condition that optimized their individual RC. In both second and third grades, students calibrated their comprehension more effectively when working in their individually optimal spacing condition. This suggests that young readers may be attuned to the efficiency of their own cognitive processing and adjust their monitoring accordingly. Such results align with theories of metacognitive development (Flavell, 1979; Veenman et al., 2006), suggesting that when text presentation facilitates efficient processing, by reducing visual crowding in second graders or preserving familiar word shapes in third graders, children are better able to monitor and judge their comprehension accurately.
These results extend our understanding of how external factors influence calibration judgments (Dinsmore & Parkinson, 2013) by demonstrating that typographical features affect not only performance but also comprehension monitoring in developing readers. This represents an important contribution to the relatively sparse literature on typography and comprehension monitoring, particularly in children. While previous research has examined font size effects on monitoring processes in word memory (Chang & Brainerd, 2022; Halamish et al., 2018), our study is among the first to demonstrate the impact of LS on comprehension monitoring in developing readers.
The finding that comprehension monitoring can be influenced as early as second grade, and are influenced by text presentation formats, has significant implications for educational interventions. It suggests that optimizing text displays could enhance not just comprehension but also the development of accurate self-monitoring, which is essential for self-regulated learning.

4.2. Reader Preferences and Educational Technology Design

Our investigation of reader preferences revealed that a larger proportion of participants in both grades preferred standard LS over increased LS, both before and after the reading task. This preference remained stable despite potentially conflicting evidence from their own performance, suggesting that familiarity may be a stronger driver of typographical preferences than performance benefits (Luna et al., 2023).
Interestingly, after completing the reading tasks, we observed a modest decrease in the preference for both LS conditions in second grade (8% decrease for standard LS and 4% decrease for increased LS) with a corresponding 10% increase in “no preference” responses. This shift, while subtle, suggests that experiencing different LS conditions may have initiated a re-evaluation of preferences in these young readers. Similar patterns were observed by Dahan-Golan et al. (2018) regarding reading modality preferences, and together with our findings, this underscores the important role of exposure to varied text presentations in shaping how such preferences are formed.

Implications

From a practical perspective, our findings suggest that educational technology platforms could enhance learning experiences by implementing adaptive typographical features. Digital reading applications could benefit from several design considerations. First, developers should consider developmental adaptivity by automatically adjusting LS based on the reader’s developmental stage, with increased spacing for beginning readers and standard spacing as holistic word recognition develops. Second, many applications already offer individual customization options, such as adjusting LS or font size, and this trend should be further expanded. Importantly, rather than relying on subjective preference alone, customization could be informed by performance feedback, thereby helping readers identify presentation formats that are associated with improved performance (e.g., accessibility features in Microsoft Word, iOS reading settings, Kindle reader). Third, developers should incorporate calibration scaffolding features that help children monitor their comprehension more accurately, potentially using optimal text display as one element of support.

4.3. Limitations and Future Directions

While our study provides valuable insights into the effects of LS on reading in digital environments, several limitations should be addressed in future research. Due to COVID-19 pandemic restrictions, we were unable to assess participants’ psycholinguistic measures and other background measures. First, reading proficiency was not assessed, which prevented examination of how reading expertise levels might moderate the effects of LS manipulations. It is important to note that, without an independent measure of reading proficiency prior to the experiment, we cannot determine whether LS manipulations influenced reading or whether existing differences in reading skills shaped children’s preferences and their ability to adapt to spacing changes. Our findings should therefore be interpreted as associations rather than causal effects.
Moreover, we did not include vocabulary, working memory, or nonverbal reasoning skills, as well as learning disabilities or attention disorders. These factors could have been integrated as covariates in the statistical models and may have provided further insight into individual differences in responsiveness to LS manipulations. Future studies should incorporate such measures to examine whether cognitive and linguistic profiles modulate the effects observed here, thereby contributing to a more comprehensive understanding of how visual text modifications interact with children’s literacy development.
Second, our assessment of reading speed during silent reading may not have captured the subtle effects that LS might have on processing efficiency. Future studies should consider using eye-tracking methodologies or oral reading tasks that might provide more sensitive measures of processing fluency and word recognition efficiency. Additionally, our measurement of preferences relied on a single question before and after the reading task. More comprehensive assessment of preferences, including qualitative interviews about the reasons underlying typographical choices, could provide deeper insights into preference formation and stability. Another limitation concerns the generalizability of our findings. While our sample of 289 participants is relatively large compared to many experimental studies in literacy research, and was drawn from multiple schools to enhance representativeness, future studies with larger and more diverse samples are warranted to confirm the robustness of these developmental patterns. Furthermore, our study focused on Hebrew, a Semitic alphabetic writing system characterized by right-to-left orientation, optional diacritics, and dense visual–orthographic forms. These features may constrain the extent to which our results can be generalized to other orthographies, such as deep alphabetic systems (e.g., English) and shallow orthographies (e.g., Spanish, Italian). Future cross-linguistic comparisons are needed to determine whether the developmental trajectory observed here extends to readers in different languages and writing systems.
Finally, another limitation relates to the reading materials. The texts were selected from children’s school textbooks that are no longer in current use to avoid any risk of prior exposure, and they were chosen by experts in literacy and reading instruction. Each text was designed to revolve around a single central idea, and preliminary analyses were conducted to ensure grade-level appropriateness and comparability in difficulty. However, we did not conduct detailed lexical or syntactic analyses (e.g., sentence length, word frequency, or idea units). Although comprehension accuracy rates were highly similar across texts, suggesting comparable levels of difficulty, future studies should incorporate systematic psycholinguistic analyses of text features to strengthen comparability and deepen understanding of how textual variables interact with typographical manipulations.

5. Conclusions

This study shows that increased LS was associated with improved RC in second-grade children, while this association diminished in third graders, reflecting a developmental progression in visual processing and reading strategies. Furthermore, children demonstrate more accurate CoC under conditions that optimize their individual reading performance, suggesting a close link between cognitive processing efficiency and comprehension monitoring in young readers. Despite that, they do not always prefer the optimal LS for their performance.
These findings have implications for the design of digital reading environments, suggesting that adaptive typographical features could enhance both cognitive performance and the development of accurate comprehension monitoring in young readers.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/educsci15101306/s1. Table S1: Summary of Studies on Letter Spacing and Reading.

Author Contributions

Conceptualization, S.D. and T.K.; Methodology, S.D.; Software, S.D.; Validation, S.D.; Formal analysis, S.D.; Investigation, S.D.; Resources, T.K.; Writing—original draft, S.D.; Writing—review & editing, T.K.; Visualization, S.D.; Supervision, T.K.; Project administration, T.K.; Funding acquisition, T.K. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the chief scientist of the ministry of education, and the Edmond J. Safra Center from Brain and Learning Disabilities, Haifa University, Israel (grant number 3-19008).

Institutional Review Board Statement

This study received approval from the Israeli Ministry of Education (protocol number 10664/19) and the Ethics Institutional Review Board at the University of Haifa.

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Texts with standard letter spacing (a) and increased letter spacing (b).
Figure 1. Texts with standard letter spacing (a) and increased letter spacing (b).
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Figure 2. Reading comprehension performance in the two letter spacing conditions. Note. * p < 0.05, ^ p < 0.10.
Figure 2. Reading comprehension performance in the two letter spacing conditions. Note. * p < 0.05, ^ p < 0.10.
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Figure 3. The effect of letter spacing on the calibration of comprehension. Note. CoC = Calibration of comprehension. OIS = optimal increased spacing group. OSS = optimal standard spacing group. EP = equivalent performance. *** p < 0.001.
Figure 3. The effect of letter spacing on the calibration of comprehension. Note. CoC = Calibration of comprehension. OIS = optimal increased spacing group. OSS = optimal standard spacing group. EP = equivalent performance. *** p < 0.001.
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Figure 4. The proportions of participants’ letter spacing conditions preferences in the second and third grades. Note. LS = Letter spacing.
Figure 4. The proportions of participants’ letter spacing conditions preferences in the second and third grades. Note. LS = Letter spacing.
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Table 1. Descriptive statistics of the optimal display subgroups.
Table 1. Descriptive statistics of the optimal display subgroups.
NStandard Spacing RC (M, Sd)Increased Spacing RC (M, Sd)
Second grade
OSS390.79 (0.25)0.45 (0.26)
OIS670.53 (0.24)0.84 (0.20)
EP570.77 (0.27)0.77 (0.27)
Third grade
OSS550.84 (0.19)0.51 (0.22)
OIS330.50 (0.25)0.85 (0.18)
EP380.70 (0.24)0.70 (0.24)
Note. RC = Reading Comprehension. OIS = optimal increased spacing group. OSS = optimal standard spacing group. EP = equivalent performance.
Table 2. t-test analyses of the effect of letter spacing on calibration of comprehension in the three subgroups.
Table 2. t-test analyses of the effect of letter spacing on calibration of comprehension in the three subgroups.
Increased LS CoC
(M, Sd)		Standard LS CoC
(M, Sd)		T Values
Second grade
OSS0.28 (0.39)−0.04 (0.36)t(34) = 5.86, p < 0.001, Cohen’s d = 0.32
OIS0.08 (0.23)0.30 (0.32)t(64) = 6.56, p < 0.001, Cohen’s d = 0.26
EP0.12 (0.25)0.10 (0.29)t(54) = 1.00, p = 0.32
Third grade
OSS0.26 (0.29)−0.07 (0.31)t(50) = 8.42, p < 0.001, Cohen’s d = 0.28
OIS−0.01 (0.23)0.32 (0.26)t(29) = 8.60, p < 0.001, Cohen’s d = 0.22
EP0.15 (0.31)0.16 (0.27)t(34) = 0.14, p = 0.89
Note. LS = Letter spacing. CoC = Calibration of comprehension. OIS = optimal increased spacing group. OSS = optimal standard spacing group. EP = equivalent performance.
Table 3. Chi squared analyses of the relation between letter spacing optimal performance subgroups and preference.
Table 3. Chi squared analyses of the relation between letter spacing optimal performance subgroups and preference.
Relation ExaminedSecond GradeThird Grade
LS optimal performance subgroups-Pre task preferenceχ2(4) = 4.12, p = 0.39χ2(4) = 0.82, p = 0.94
LS optimal performance subgroups-Post task preferenceχ2(4) = 5.20, p = 0.27χ2(4) = 1.32, p = 0.86
Pre task preference-Post task preferenceχ2(4) = 54.49, p < 0.001χ2(4) = 66.69, p < 0.001
Note. LS = Letter spacing.
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Dotan, S.; Katzir, T. Effects of Increased Letter Spacing on Digital Text Reading Comprehension, Calibration, and Preferences in Young Readers. Educ. Sci. 2025, 15, 1306. https://doi.org/10.3390/educsci15101306

AMA Style

Dotan S, Katzir T. Effects of Increased Letter Spacing on Digital Text Reading Comprehension, Calibration, and Preferences in Young Readers. Education Sciences. 2025; 15(10):1306. https://doi.org/10.3390/educsci15101306

Chicago/Turabian Style

Dotan, Shahar, and Tami Katzir. 2025. "Effects of Increased Letter Spacing on Digital Text Reading Comprehension, Calibration, and Preferences in Young Readers" Education Sciences 15, no. 10: 1306. https://doi.org/10.3390/educsci15101306

APA Style

Dotan, S., & Katzir, T. (2025). Effects of Increased Letter Spacing on Digital Text Reading Comprehension, Calibration, and Preferences in Young Readers. Education Sciences, 15(10), 1306. https://doi.org/10.3390/educsci15101306

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