1. Introduction
Climate change is considered one of the greatest challenges of our time and an even greater challenge for future generations. It poses severe threats to ecosystems, biodiversity, and human livelihoods. Counteracting climate change and protecting our ecological livelihoods is a prerequisite for ensuring social stability and economic prosperity for all generations worldwide [
1]. To achieve this global aspiration for a sustainable society, the United Nations adopted the Sustainable Development Goals (SDGs) as part of the 2030 Agenda. These include the goal “Climate Action” (SDG 13), which directly emphasizes the need for urgent action to combat climate change and its impacts. In order to achieve this goal on an environmental, economic, and social dimension, quality education is needed to empower future generations. Accordingly, the need for Quality Education (SDG 4) was established in 2015, which includes the subgoal of promoting education for sustainable development (ESD), making schools responsible for its mandatory implementation. This subgoal also focuses on systems thinking, which UNESCO [
2] (p. 10) defined as the ability “to recognize and understand relationships [and] to analyze complex systems”.
This type of thinking is considered to be a key competence for ESD [
1,
3,
4,
5] because it promotes the understanding of relationships in complex systems for the development of sustainable solutions in meeting the challenges mentioned above. Early age-appropriate development of this key competence is necessary, given that neither adults nor children demonstrate intuitive systems thinking skills [
6]. However, research on systems thinking in elementary school (i.e., Grades 1 to 4 in most federal states in Germany and as it pertains to the current study) is limited compared to higher grade levels [
7,
8]. In their systematic review of empirical studies on systems thinking, Budak and Ceyhan [
7] found only one relevant study out of 27 involving elementary school students, highlighting the need for further research in this age group.
One reason for this gap in the literature is the challenge of thematizing complex systems (such as the climate system) without mentally overloading elementary school students. The use of system models, whether analog, computational, or simulation, has proven to be a suitable approach for this in previous research [
9,
10,
11,
12,
13,
14,
15,
16], even in elementary school [
3,
17,
18]. System models allow for the visualization of a variety of system elements (structure) and interactions (dynamics) within the system. However, it is unclear which type of system model is particularly conducive to optimally developing systems thinking in elementary school. Evidence supports the benefits of both qualitative (e.g., [
9,
19]) and quantitative system models (e.g., [
10,
20,
21]), yet a direct comparison of these models within the same intervention has not been conducted. Furthermore, it is open whether time representations, which should be integrated into system models [
22], given that students often lack an intuitive grasp of time dimensions [
6], are conducive to learning for elementary school students or rather overwhelming.
Building on the evidence that the use of system models is conducive to learning, even at the elementary school level, the purpose of this study was to investigate whether there are advantages to a particular type of system model. Specifically, this study examined the effects of using alternative system models (qualitative vs. quantitative) with varying visualizations of temporal developments of climate change in the development of different facets of systems thinking in elementary school students. To answer our research questions, different system models (a qualitative system model without time representation vs. a qualitative system model with time representation vs. a quantitative system model with time representation vs. the control group) were used in a five-lesson classroom intervention study with fourth graders to foster systems thinking on climate change. We examined whether these models differ, in general, and whether differences exist between different facets of systems thinking. Additionally, we investigated whether any differences could be attributed to the situational interest in the system models and student interaction with the respective system model.
2. Theoretical Background
People interact daily in social, technical, economic, and ecological systems. Such systems are complex with interacting elements that form an organized unit (e.g., [
5,
23]). The actions that take place within them are often simultaneous and uncoordinated such that the effects are often not transparent. That is, systems can be complex and sometimes unpredictable in their behavior, for example, through feedback loops, dynamics, nonlinearities, and emergence [
24,
25]. Educating students to act responsibly in an increasingly complex world necessitates a systemic approach to the environment, given that students and even adults cannot intuitively recognize the just-mentioned properties of systems [
6]. For this reason, systems thinking needs to be fostered and to be assigned a crucial role in science lessons [
2,
26].
Students should be enabled to understand not only superficial structural features but also deeper dynamic behaviors of systems, which experts are able to comprehend by including all components—structure, behavior, and function [
27]. This level of understanding requires the identification of system elements as well as their properties and interrelationships [
28,
29,
30]. An effective way to meet these requirements is systems thinking, which is not just a “coherent understanding” of systems but rather a way of thinking to explain, understand, and predict natural phenomena [
10,
31]. In line with this distinction, Mischo and Rieß [
32] (p. 348f.) defined systems thinking as the cognitive “ability to recognize, describe, and model (e.g., to structure, to organize) complex aspects of reality as systems. This includes the ability to determine system elements and interrelationships, to grasp temporal dimensions (dynamics) and the ability to provide explanations, make predictions, and [derive recommendations for action] on the basis of one’s own modeling”.
An increasing number of empirical studies on systems thinking have been published, especially in recent years. Despite the substantial body of studies, no common terminology has yet been established. Different terminologies coexist, some of which are used synonymously but some of which arise from different conceptualizations of systems thinking [
7,
8,
33]. One of the main reasons for this lack of common terms is the interdisciplinary nature of the respective research. Different disciplines analyze and interpret systems from different perspectives and with different focuses. In biology, topics range from microbiological systems, such as cells [
34], to macroecological systems such as swamps [
10], forests [
11], and habitat models such as that of the stork [
17]. However, geophysical systems, such as the water cycle [
35] and economic systems such as the pizzeria [
10] or chocolate from an economic–social perspective [
3], have also been addressed. These disciplinary differences lead to different systemic perspectives. For example, biologists often focus on natural systems, whereas geographers, according to Rempfler and Uphues [
4], integrate a socio–spatial perspective alongside the natural spatial perspective. Systems vary in their openness or closure as well as in their structural and behavioral complexity. Despite the different perspectives, a consensus exists among the disciplines on the fundamental characteristics of the construct. Specifically, the various disciplines agree on its multidimensional nature [
36] as well as on the need to differentiate between a static representation of the system and the interactions among its individual components caused by interrelationships. This shared understanding of systems also results in a consensus about the skills required for effective systems thinking. Three core abilities are commonly recognized as follows: identifying system organization, analyzing system behavior, and system modeling [
7,
30].
Several competence models have been developed. The following chapter focuses on identifying a model that can be implemented in practice and is applicable for the purposes of this study. Subsequently, the results of intervention studies are presented, which clearly show the existing research gap.
2.1. Identification and Adaption of a Competence Model for Systems Thinking
For the purpose of this study, we had three requirements for the chosen competence model: (1) The competence model should account for modeling skills because elementary school students in particular need to be supported in their mental modeling when dealing with complex scientific phenomena that cannot be directly observed such as the climate system; (2) suitability for elementary school should exist or be achievable through minimal adaptations; and (3) the competence model should be suitable for use in intervention studies. We examined the competency model by Ossimitz [
9], the structural model for systems competence by Sommer [
17], the System Thinking Hierarchical (STH) Model by Assaraf and Orion [
18,
35], the Structure–Behavior–Function (SBF) Model by Hmelo-Silver and Liu [
37] in combination with the Components–Mechanisms–Phenomena (CMP) Model by Hmelo-Silver et al. [
12], the competence model for systems thinking by Bollmann-Zuberbühler et al. [
19], the competence model for systems competence by Rempfler and Uphues [
4], and the heuristic structural competence model by Rieß et al. [
5].
After applying the three criteria, the heuristic structural competence model by Rieß et al. [
5] resulted in the most suitable model. This model places a particular focus on the modeling of systems (requirement 1), which has been established in climate research and has shown to be conducive to learning in the above-mentioned intervention studies as well as in the overarching and pedagogical principles of developing systems thinking by Assaraf and Knippels [
16]. In addition, this competence model addresses the entirety of systems thinking, from secondary school to adulthood, and can be easily adapted to the elementary school level (requirement 2). Following Yoon et al.’s [
38] call for more comparative research on teaching and learning about complex systems in the sense of holistic spiral curricular teaching of science subjects, we intended to investigate if the model is also suitable for elementary school. Most recently, the heuristic structural competence model has shown to be practicable in intervention studies at the secondary school level [
14,
39], among student teachers [
40,
41], and in further teacher training [
42] (requirement 3).
The version of the heuristic structural competence model [
5] adapted to the elementary school target group is presented below (
Table 1). The original competence model consists of four dimensions, each with four sub-capabilities. Given the focus on solving complex problems with the help of system models (dimension 3), we selected only the sub-capabilities that are central precursor capabilities for the target capabilities in dimension 3. Secondly, the time frame of this study of five lessons (each 45 min) would preclude the effective use of all sub-capabilities. For these reasons, we selected six sub-capabilities and adapted them for fourth graders in elementary school (
Table 1). Note that the original version of the heuristic structural competence model of systems thinking [
5] includes a fourth dimension, which focuses on the evaluation of system models. This competence is aimed at experts in systems science and is thus not relevant for elementary school students. We therefore omitted this dimension.
The requirements of each competence dimension are briefly described below, along with explanations of how they have been adapted to the elementary school level, accompanied by concrete examples that illustrate the level of requirements.
Dimension 1 addresses declarative, conceptual system knowledge, including basic knowledge of systems theory (e.g., [
23]) as well as knowledge of areas of reality that can be considered as systems. Regarding the target group, it should be noted that this fundamental systems science approach is a basic knowledge. In an initial examination of systems at the elementary school level, aspects of complex systems such as multi-causality, feedback, dynamic complexity [
9], nonlinearity, emergences, or dissipative structures [
43] can only be addressed to a limited extent in favor of a basic understanding. For example, in this dimension, students should be able to describe a system in general terms by explaining that it consists of several elements that are connected to each other.
Dimension 2 is characterized by the ability to model systems and thus the ability to understand and construct different types of system models. Note that elementary school students should first be encouraged to understand before being able to construct system models, that is, starting with familiar forms of representation (e.g., text), then reducing features (e.g., word model), to finally understanding increasingly abstract system models (e.g., connection circle). For this study, the influence diagram method was replaced with the connection circle method because this method has already been established in elementary school [
19]. A particular advantage over the influence diagram is the external structure of a circle, which is used for all system models and therefore simplifies system modeling. The system elements are arranged around the circle, and effect relationships are indicated by arrows with corresponding effect signs that denote the quality of the effect. For example, this dimension requires students to analyze information from a text and identify related arrow diagrams (as precursor models for qualitative and quantitative system models).
Dimension 3, which is the target dimension of this research, is characterized by solving complex problems (i.e., climate change in the current study) with the help of system models. The aim is to give simple explanations for system behavior, make predictions, and design simple technologies with either qualitative or quantitative system models. For example, this dimension requires students to explain how climate change affects sea levels over time using a qualitative or quantitative system model.
Many of the competency models presented have been used in intervention studies to evaluate which teaching–learning methods, tools, and teaching units are effective in developing systems thinking. In the following chapter, a selection of relevant studies is presented to highlight existing research approaches. Based on this review, the research gap is then identified, which is addressed by this study.
2.2. Fostering Systems Thinking
To understand complex systems, grasping the structure, behavior, relationships, interactions, feedback, and dynamics within the system is essential [
44]. However, numerous studies have shown that students face cognitive challenges when dealing with complex systems [
45] and have difficulties understanding interactive and especially dynamic aspects of complex systems beyond visible structures [
46], particularly when cause and effect are spatially or temporally separated [
6]. Given that systems thinking is not a natural development in students [
6], it must be actively fostered to help students overcome these challenges and act appropriately within systems. Intervention studies have examined which approaches are particularly effective in developing systems thinking. Assaraf and Knippels [
16] identified four overarching pedagogical guidelines and scaffold strategies from a variety of empirical studies that are particularly effective when embedded in a well-designed learning environment. Apart from the use of system language, cross-level reasoning, and authentic inquiry approach, modeling has emerged as a promising approach, which is the focus of this study. Models or modeling activities can exist in various forms: they can be mental, verbal, or qualitative, as seen in pen-and-paper modeling activities (e.g., concept map, connection circle, and causal loop diagram). They can also be formal, like most quantitative models, which utilize numerical data and systems of equations (e.g., (interactive) computer simulations) [
9,
16,
22].
Studies have used qualitative system models or modeling activities to assess and to foster systems thinking. Concept maps and drawings are tools for modeling complex systems, and they offer the opportunity to visualize complex biological phenomena or problems and to explore system characteristics [
16]. In this context, causal loop diagrams are considered a “standard tool” of systems thinking [
9], whereas the connection circle has established itself as a simplified form of causal loop diagram in elementary schools [
19]. Hogan [
47] used a food web analysis task before and after a month-long, hands-on unit in which 11-year-old students constructed, observed, and manipulated mini-ecosystems. He found that students mostly considered direct effects and rarely indirect effects, a finding also reported by Grotzer [
48]. In Sommer’s [
17] 10 h intervention study on the white stork system in the third and fourth grade, students improved their system organization skills through classroom engagement with concept maps and a computer game (combination of qualitative and quantitative approaches), as evidenced by the significant increase in the number of system elements and the networking performance in concept maps. However, the students still showed a lack of understanding of system dynamics. Ben-Zvi Assaraf and Orion [
18] also used concept maps in the fourth grade on the topic of the water cycle as part of a holistic teaching unit, in addition to experiments, outdoor activities, and knowledge integration activities. The study showed that students made significant progress in identifying system components and relationships after the intervention. The authors recommend that elementary schools should focus on recognizing relationships between system components and dynamic relationships as a basis for further development in secondary education.
In contrast to the qualitative models, the impact of quantitative system models (mainly in the form of simulations) on systems thinking has been examined. A simulation is a “tool used to explore a real-world […] system by approximating the behavior of the […] system” [
49] (p. 2), which involves the manipulation of parameters to model the system. Research into the effectiveness of computer simulations in science education shows that the use of computer simulations in the classroom can be effective in science learning, depending on how they are used [
20,
21,
50]. This finding also applies to the teaching of systems thinking with simulations. At this point, we would like to point out that there are just a few studies on quantitative system models to promote systems thinking in elementary education. In order to provide a broader overview, we have included relevant studies from higher grade levels. The findings from these studies can at least be partially transferred to the elementary level. Bergan-Roller et al. [
13] demonstrated the effectiveness of a simulated computational model lesson on undergraduate biology students’ systems thinking skills and conceptual knowledge. The positive impact of simulations on systems thinking in learning environments was also examined in college students [
51] and in secondary school students [
9,
11,
12,
14,
15,
52]. In the primary sector, Ceresia [
53] developed the interactive learning environment Sunny Island, a comprehensive learning environment centered around a simulation, designed for fourth- and fifth-grade elementary school students. Initial qualitative analyses showed a positive effect on systems thinking, but the study was a pilot, and the final results have not yet been published. Evagorou et al. [
10] investigated the impact of a simulation-based learning environment on the marsh ecosystem on the development of systems thinking in fifth and sixth graders. The results show that students improved in identifying the system’s structure and simple linear causal relationships. However, students showed low competence in considering the effects of elements on other elements beyond simple linear effects or on the whole system and in considering temporal perspectives.
Overall, we conclude that for the primary sector, (a) elementary school students as early as first grade can already be supported in developing systems thinking skills, (b) the use of system models (and modeling activities) has always been embedded within teaching units, (c) both types of system models have shown to be beneficial to learning; a comparative investigation (qualitative vs. quantitative) in the same teaching and learning environment has yet to be conducted. Furthermore, evidence has shown that (d) elementary school students, as well as novices in general, refer primarily to the structure and simple effects of a system but not to more complex properties such as temporal developments. Given that students show a lack of intuitive understanding of time dimensions [
6], this temporal perspective should be considered in system models [
22]. However, in elementary school it is open whether the additional representation of temporal development is conducive to learning or whether it is overwhelming [
16].
2.3. The Present Study
As described in the previous chapter, interventions aimed at promoting systems thinking have been shown to be effective when embedded in teaching units. To ensure the effectiveness of the teaching unit in this study, it was designed using the Model of Problem-Oriented Teaching and Learning (MopoLL) by Rieß and Mischo [
54]. Based on Van Merriënboer’s 4C/ID model [
55,
56] the authors developed a teaching method aimed at the evidence-based promotion of dynamic problem-solving competence and explicitly emphasized the model’s suitability for promoting systems thinking. The MopoLL consists of six strategically arranged and sequential phases, as shown in
Figure 1.
In Phase (1), named Presentation of the Problem and First Attempts at a Solution, students are confronted with a scientific problem and attempt to generate a solution based on their prior knowledge. They recognize that the problem is theoretically solvable but requires additional or deeper competencies and knowledge. These target criteria (competencies, knowledge) are determined in Phase (2), named Target Determination, where an overview of the unit’s structure is made transparent. In Phase (3), named Providing Technical Background Knowledge and Presenting a Successful Problem Solution, instructive explanations are given to facilitate the knowledge construction process. Subsequently, in Phase (4), named Independent Problem Solving with Decreasing Support, students increasingly solve problems similar to the initial problem independently. In Phase (5), named Presentation, Articulation, and Reflection, students present their learning outcomes and reflect on the learning process in relation to the previous learning phases. Finally, in Phase (6), named Practice, Transfer, and Consolidation, the newly acquired skills and knowledge are applied to related problem-solving tasks.
2.4. Research Question and Hypotheses
There is evidence suggesting that system models foster systems thinking. However, to date, no fundamental research has been carried out at the elementary school level to determine whether qualitative or quantitative system models are more suitable, especially for the representation of time (dynamic processes) in complex systems such as the climate system. Consequently, the aim of this study was to investigate the effects of using alternative system models with varying visualizations of temporal developments in a problem-based teaching and learning environment on developing different facets of systems thinking in elementary school students.
We assumed the following after the intervention:
All experimental groups would improve their general systems thinking in comparison to the control group.
Students working with a quantitative system model (experimental group 3) would outperform students who work with a qualitative system model (experimental groups 1 and 2), especially in dimension 3 (solving problems using system models).
Students working with a system model with time representation (experimental groups 2 and 3) would perform better in dimension 3 (solving problems using system models) than students who work with a system model without time representation (experimental group 1).
Students working with a qualitative system model would perform better in dimension 2 (modeling systems).
4. Results
4.1. Systems Thinking
This section presents the results on systems thinking. Furthermore, the formulated hypotheses will progressively be revisited and evaluated. Note that the hypotheses in this section are presented in a summarized form. For detailed descriptions see
Section 2.4.
The data were analyzed according to the descriptions of the analysis strategy above (see
Section 3.5). An ANCOVA with the overall score of systems thinking revealed a significant difference between all groups,
F(3, 288) = 18.67,
p < 0.001, η
p2 = 0.16. We found no significant influence of duration of intervention on systems thinking,
p = 0.29. Post hoc tests (Sidak-corrected) revealed a significant difference between QUAL_NT and CG,
Mdiff = 6.00,
p < 0.001,
d = 1.24; QUAL_T and CG,
Mdiff = 6.10,
p < 0.001,
d = 1.13; and QUAN_T and CG,
Mdiff = 4.29,
p < 0.001,
d = 0.84. No significant differences could be found across all competence dimensions between the three experimental groups. The corresponding hypothesis, Hypothesis 1, stated that “All experimental groups would improve their general systems thinking in comparison to the control group”. This hypothesis can be confirmed because all experimental groups differ significantly from the control group, with a large effect size across all dimensions. The key values for the individual competence dimensions are shown below (see
Table 2) and described in the following.
In dimension 1 (declarative/conceptual system knowledge), a significant difference between all groups was found, F(3, 288) = 6.13, p < 0.001, ηp2 = 0.06. Post hoc tests (Sidak-corrected) revealed a significant difference between QUAL_NT and CG, Mdiff = 1.27, p = 0.002, d = 0.58; QUAL_T and CG, Mdiff = 1.25, p = 0.002, d = 0.64; and QUAN_T and CG, Mdiff = 1.21, p = 0.004, d = 0.59. No significant differences could be found between the three experimental groups.
In dimension 2 (modeling systems), a significant difference between all groups was found, F(3, 288) = 6.87, p < 0.001, ηp2 = 0.07. Post hoc tests (Sidak-corrected) revealed a significant difference between QUAL_NT and CG, Mdiff = 0.72, p = 0.029, d = 0.47, and QUAL_T and CG, Mdiff = 0.87, p = 0.004, d = 0.56, but not between QUAN_T and CG, Mdiff = 0.49, p = 0.233, d = 0.33. No significant differences could be found between the three experimental groups. The corresponding hypothesis, Hypothesis 4, stated that “Students working with a qualitative system model would perform better in dimension 2 (modelling systems)”. This hypothesis can be confirmed because the groups with the qualitative system models (QUAL_NT and QUAL_T) differed significantly from the control group on competence dimension 2, whereas no difference was found in the group with the quantitative system model (QUAN_T).
In dimension 3 (solving problems using system models), a significant difference between all groups was found, F(3, 288) = 7.39, p < 0.001, ηp2 = 0.07. As with dimension 2 (modeling systems), post hoc tests (Sidak-corrected) revealed a significant difference between QUAL_NT and CG, Mdiff = 2.45, p < 0.001, d = 1.07, and QUAL_T and CG, Mdiff = 1.90, p = 0.002, d = 0.52, but not between QUAN_T and CG, Mdiff = 1.25, p = 0.097, d = 0.48. No significant differences could be found between the three experimental groups. The first corresponding hypothesis, Hypothesis 2, stated that “Students who work with a quantitative system model (experimental group 3) would outperform students who work with a qualitative system model (experimental groups 1 & 2), especially in dimension 3 (solving problems using system models)”. This hypothesis must be rejected. Although no significant differences were found across all dimensions between participants who worked with a qualitative and participants who worked with a quantitative system model, differences occurred on a descriptive level. In addition, competence dimensions 2 (modeling systems) and 3 (solving problems using system models) showed that only the groups working with the qualitative system models differed significantly from the control group but not the group working with the quantitative system model. The second corresponding hypothesis, Hypothesis 3, stated that “Students who work with a system model with time representation (experimental groups 2 & 3) were expected to perform better in dimension 3 (solving problems using system models) than students who work with a system model without time representation (experimental group 1)”. This hypothesis must be rejected because the opposite occurred. The group that worked with the (qualitative) system model without time representation (QUAL_NT) differed significantly from the control group with a large effect. The groups that worked with system models with time representation performed worse. The qualitative system model (QUAL_T) differed significantly from the CG with a medium effect and the quantitative system model only at the descriptive level but not significantly.
4.2. Climate Knowledge
The data were analyzed according to the descriptions of the analysis strategy in
Section 3.5. To calculate the differences in climate knowledge between the experimental conditions and the control group, an ANCOVA was conducted across all groups. The analysis revealed a significant difference in the overall score of climate knowledge between all groups,
F(3, 288) = 26.08,
p < 0.001, η
p2 = 0.21. Post hoc tests (Sidak-corrected) revealed a significant difference between QUAL_NT and CG,
Mdiff = 5.25,
p < 0.001,
d = 1.31; QUAL_T and CG,
Mdiff = 5.21,
p < 0.001,
d = 1.65; and QUAN_T and CG,
Mdiff = 4.52,
p < 0.001,
d = 1.11. No significant differences could be found between the three experimental groups. The key values for the learning gains in climate knowledge are shown below (see
Table 3).
4.3. Interest in and Practical Use of the System Model
An ANCOVA with the overall score for the triggered situational interest in the system model revealed a significant difference between all experimental groups,
F(2, 201) = 3.63,
p = 0.028, η
p2 = 0.35. Post hoc tests (Sidak-corrected) revealed a significant difference between QUAL_NT and QUAN_T,
Mdiff = 2.23,
p = 0.032,
d = 0.32, but not between QUAL_NT and QUAL_T and between QUAL_T and QUAN_T. No significant differences were observed in maintained interest between the experimental groups,
F(2, 201) = 1.38,
p = 0.254, η
p2 = 0.01. The key values for the interest triggered and maintained in the system model are shown below (see
Table 4).
The detailed results of an additional mediation analysis are not reported here because the nonsignificant mediation paths provide no additional information for interpreting the main effects (see
Appendix B).
As described in
Section 3.3.3, the QUAN_T group was given the additional item “Sometimes I played with the app and did not work on the tasks in the research booklet” and 14.1% answered “not true at all”, 21.9% answered “rather not true”, 15.6% answered “rather true”, and 48.4% answered “exactly right”.
5. Discussion
The goal of this study was to investigate the effects of using alternative system models (qualitative vs. quantitative) with varying illustrations of temporal developments (dynamics) on different facets of systems thinking about climate change in elementary school students. To measure learning effects, systems thinking based on the heuristic structural competence model [
5] was measured before and after a five-lesson classroom intervention. Before discussing the results, the domain-specificity of systems thinking should be noted [
63]. In the current study, we used the topic of climate change, with the requirement level adapted to fourth graders. The results presented should be interpreted in this way.
Our research has shown that all system models used, whether qualitative or quantitative, with or without time representation, have been successful in fostering systems thinking about climate change in elementary school students compared to the control group, which underlines the well-known benefits of system models for developing systems thinking [
16], especially on sustainability issues of complex systems [
64]. A closer look reveals differences between the system models on a descriptive level, but no clear advantage has been shown for one particular system model across all competence dimensions. All experimental groups in the current study improved relatively equally in declarative/conceptual system knowledge (dimension 1) between the two measurement times, but the connection circle, with and without time representation, showed advantages over the digital simulation model with time representation in modeling systems (dimension 2) and solving problems using system models (dimension 3). Overall, the connection circle with time representation led to the highest increase in competence. At this point, it is important to note that while time representation may be an important factor, there may also be potential confounding elements, such as better or more graphics in the system models with time representation and the additional interactivity in the quantitative system model, that influence the outcome. Future studies should consider isolating these variables to gain clearer insights. Comparison with other intervention studies reveals similarities: All of the models used were able to significantly improve systems thinking between measurement points. Similarly to our study, the simulation model performed worse in Brockmüller’s [
14] study with students in grades 10–12. However, combining the simulation model with an analog model significantly increased its effectiveness. The effectiveness of combined learning strategies (simulation + lessons or analog models) is also highlighted by Rieß and Mischo [
11] and Dierkes [
20].
The results also showed that interest in all system models was very high. In particular, the digital simulation model with time representation was able to trigger short-term interest but could not be maintained over time to that extent. According to Eseryel et al. [
65], a loss of interest is not necessarily equivalent to a decrease in engagement in problem solving. However, the advantage of the digital simulation in triggering interest is accompanied by a clear tendency to play aimlessly, an effect that was already reported in a review by de Jong and van Joolingen [
61]. Ultimately, the results showed that this system model led to no increase in learning outcomes in systems thinking. Thus, interest in the system model has no explanatory power for the differences in systems thinking, as indicated by a mediation analysis that showed no significant effects.
The results suggest that no single system model optimally improves systems thinking across all dimensions. As the competence dimensions increase, especially in the challenging third dimension (solving problems using system models), a decrease in the complexity of the system model seems to be more conducive to learning. Evidence of this assumption is provided by the strong performance in dimension 3 (solving problems using system models) of the qualitative system model without time representation (low complexity), whereas the high standard deviation of the qualitative system model with time representation (medium complexity) suggests that the time representation benefits some students, yet proves to be a hindrance for others. This link is supported by Hmelo-Silver and Pfeffer’s [
27] study, which shows that novices tend to focus on less complex, static components, suggesting that reduced complexity in the model enhances comprehension and problem-solving skills for learners of different levels of competence. Additionally, the quantitative system model with time representation (high complexity) achieved the poorest results. This finding is in line with the conclusions of Assaraf and Knippels [
16], stating that computer-based simulations are conducive to learning, but the high cognitive load of simultaneous representations and information can be disadvantageous to learning. This effect seems to be particularly evident in fourth graders, given that the group in our study that worked with the computer-based simulation performed the worst, contrary to our hypothesis and to other promising studies on the use of simulations to foster systems thinking in older students (e.g., [
10,
13,
15,
51]). However, the real effect of this digital simulation model could also be masked by the way it was used (aimless play), which should be seen as a limitation of this study. Although our procedure tried to minimize aimless play (e.g., prior exploration phase, precise tasks), this effect still occurred. The way in which young students interact with digital system models could be investigated in future research, for example, by examining log files or screen recordings. Following the findings of Brockmüller [
14], the extent to which an additive use of system models would be useful for elementary school students should also be investigated, for example, for the differentiated promotion of the different competence dimensions.
In line with previous research (e.g., [
17,
30,
66]), we found comparable effects between subject knowledge and systems thinking. All experimental groups showed significant learning gains in climate knowledge. On a descriptive level, the connection circles, especially the connection circle with time representation, showed advantages identical to the results on systems thinking. Thus, domain-specific knowledge not only predicts the ability for systems thinking, but systems thinking also helps to structure and thereby retain newly acquired knowledge (here on climate change).
Finally, two practical limitations of the present intervention should be addressed. Firstly, for reasons of comparability, we refrained from going through the teaching processes initiated by the teacher. Specifically, this means that Phases 5 (presentation, articulation, and reflection) and 6 (practice, transfer, and consolidation) of MopoLL [
54] were not part of the intervention (see
Section 3.4). Yet, these phases are highly relevant for learning success because teachers can provide support in terms of structuring knowledge, and discussing the learning content can encourage in-depth exploration and lead to deeper understanding. Based on the findings of Grotzer and Bell Basca [
67], the discussion of system models content would therefore be expected to lead to further learning gains than those shown in our study. It is likely that additional individual feedback during the use of the system model would also improve the performance of the digital simulation with time representation [
21,
50]. Secondly, for practical reasons, not all sub-capabilities of the heuristic structural competence model of systems thinking [
5] could be addressed in this study. Future research could complete the sub-capabilities not considered here, given that the fourth competence dimension (evaluation of system models) is likely to be too complex for the elementary level.
Overall, our findings suggest that the qualitative system models of climate change were more effective than the quantitative system model on fostering systems thinking for elementary school students. The combination of the qualitative system model with time representation proved to be the most effective in the lower competence dimensions (declarative/conceptual system knowledge and modeling systems). For the higher competence requirements of solving complex problems, reducing the complexity of the qualitative system model (no time representation) seems to be more conducive to learning for fourth graders.