As a result of international comparative studies, educational reforms in several countries have focused on developing and implementing National Education Standards (NES) in science education [1
]. To state these NES more precisely, several dimensions were formulated. In Germany, four dimensions were established by the Conference of the Ministers of Education (KMK): content knowledge, scientific inquiry, communication, and scientific judgment [4
]. More specifically, content knowledge represents a subdimension of a subject-specific content-related dimension and the other three dimensions are actually subdimensions of a process-related dimension [4
]. A process-related dimension takes into account several constructs of scientific inquiry and scientific reasoning [2
] and has become increasingly important. Within this process-related dimension of NES, scientific methods and the use of models in instruction were included as part of the learning in scientific inquiry; [2
]. In this regard, models and modeling play a central role in science instruction and science education [10
]. Additionally, science instruction should foster students’ understanding of models and modeling in science [1
]. Therefore, models can be seen as “representations of objects, phenomena, processes, ideas and/or their system” [12
] (p. 7). Models are a representation of real and mental objects [13
]. In contrast to representations, models are also used to generate information about the real objects [13
]. They can be used for testing ideas and drawing conclusions on the original object. They can be seen as important research tools in science and sciences instruction and have an interpretative nature [14
]. Therefore, models in contrast to representations can be manipulated and explain the original through examination [15
] However, activities for students or teachers to use models in classroom are hardly present [16
]. Several studies already showed that using models in instruction has a more significant effect on students’ achievement, compared to other teaching materials, for example [17
]. However, aspects of (1) which way models should be used in biology instruction to achieve higher students’ achievement in biology, and (2) which dimensions of professional knowledge do teachers need for using models in leading to an increase in students’ knowledge in biology, have remained unclear.
Therefore, this mixed-methods study with an explanatory sequential design, [21
], first analyzed the effects of subject-specific knowledge dimensions, and different characteristics of the model use in biology instruction on students’ achievement. Additionally, in order to describe in more detail the use of models, which fosters students’ achievement in biology, contrasting extreme cases of teachers were used in the qualitative phase of the study. In the following sections, we review the previous studies concerning the use of models in science instruction, the effects of teachers’ pedagogical content knowledge (PCK) and content knowledge (CK) on model use, as well as the effects of using models on students’ achievement.
1.1. The Nature and Purpose of Models in Science Instruction
The aim of science education is to foster students’ learning of science, learning about science, and learning to do science [22
]. Harrison and Treagust [23
] assumed that students learn and understand science in an elaborate way as they learn and understand models created by scientists. Therefore, using models in instruction is one important teaching strategy in science; [24
]. Nevertheless, there is still no general point of view of how ‘models’ can be defined [25
]. According to a simple definition, models are “representations of objects, phenomena, processes, ideas and/or their system” [12
] (p. 7). In instruction, teachers use models to make dangerous and complex scientific phenomena accessible for students and to illustrate certain aspects of a content area [13
]. While introducing NES in science, for example, in Germany [2
], and in the U.S. [3
], the demand for using models as tools for scientific inquiry, for example, for predicting scientific phenomena, becomes even more important (e.g., [9
]). Through models, complex phenomena are illustrated for students in an understandable way [14
]. Therefore, models can support the development of mental representations and conceptual ideas of the phenomenon [35
]. Additionally, modeling illustrates the work of researchers in science and scientific inquiry for students. Both aspects foster the development of students’ scientific literacy as a main goal of scientific instruction. However, such implementation of instruction using models is hardly represented in science classrooms [9
]. Additionally, Gogolin and Krüger found that “[s] tudents’ levels of understanding of the nature and the purpose of models increase only little across grades” [39
] (p. 1).
1.2. Teachers’ Domain-Specific Professional Knowledge Including Knowledge about Models and Modeling in Science
The use of models is one of the biology-specific teaching strategies. Therefore, the knowledge about models and modeling can be described as an important facet of teachers’ pedagogical content knowledge (PCK); [24
]. PCK is part of teachers’ domain-specific knowledge besides content knowledge (CK) [24
]. CK includes knowledge about subject-specific content and the conceptual understanding of this content; [41
]. In contrast, PCK mainly consists of knowledge about students’ misconceptions as well as knowledge about teaching strategies and representations, for example [41
]. Theoretically, teachers with high PCK are able to make content understandable for students [44
Teachers’ PCK of models and modeling consists of several further parts. Schwarz [30
] described three aspects, which can be taken into account in this context: ‘Knowledge of science’, ‘knowledge of science learners’ and ‘views of effective science teaching’. A high knowledge of science is expressed in the understanding of models as a generative tool, which can be revised, and their importance in inquiry and application [45
]. Knowledge of science learners describes the knowledge of teachers about students’ prerequisites, which they need, when they learn aspects of scientific reasoning by models [46
]. Views of effective science teaching include the use of models for scientific inquiry. Therefore, individual concepts of the learning content will be illustrated by multiple perspectives [46
]. On the basis of these three aspects of teachers’ PCK about models and modeling, it becomes clear that teaching with models has to be in line with the demands of National Education Standards [2
]: fostering students’ understanding of science through elaborate use of models in instruction. Elaborate use of models in instruction is characterized by using models as tools of scientific reasoning, formulating scientific research questions and hypotheses, revising models based on empirical data, and reflecting on them critically [47
]. Therefore, a “teacher’s knowledge and views will significantly impact her instructional planning and assessment practices using models” [46
] (p. 4). It seems obvious that teachers’ PCK is important for effective implementation of models in instruction to foster students’ achievement. In order to use models in a way that helps students to develop elaborate understanding of models and modeling in science, science teachers need understanding of as well as knowledge about models and modeling [48
Several studies already have focused on describing knowledge about models and modeling of preservice and in-service teachers [16
] or developed professional development programs on this topic [49
]. These studies described the knowledge structure of preservice or in-service teachers and possibilities to improve their limited and inadequate knowledge about models and modeling. First of all, it seems reasonable to identify effects of teachers’ knowledge dimensions on their use of models in instruction and to analyze effects of different facets of PCK and CK afterwards. However, effects of different dimensions of teachers’ knowledge on model use in instruction were seldom considered. Before our study, some studies which described and fostered teachers’ knowledge about models and modeling as part of their PCK were conducted (e.g., [35
]). However, comparison of different knowledge dimensions and their individual effects on using models in instruction was hardly taken into account.
1.3. Effects of Using Models in Instruction on Students’ Outcome
As students develop an elaborate understanding of models and modeling in science through using models elaborately in their learning [15
], elaborate model use should positively affect their learning outcomes in biology. Several intervention studies provided the first indications of the effect of model use on students’ learning (e.g., [17
]). Students working with models showed higher abilities in answering knowledge-transferring tasks and generated a more elaborate understanding of models and modeling in science [34
]. Additionally, students learned new concepts more easily (e.g., [56
]). Furthermore, students who worked with models learned more accurately and appropriately than did other students without using models (e.g., [17
]). The study of Barak and Hussein-Farraj [17
] additionally indicated that students developed higher level thinking when they worked with models on their own during instruction. Barak and Hussein-Farraj [17
] defined higher level thinking as the students’ ability to transfer between several representations with various dimensions. Several aspects of model use in instruction, which is effective for fostering students’ achievement, were derived from empirical studies and theoretical assumptions and were summarized in the construct elaborate model use (ELMO) of [47
]. ELMO comprises (1) a characterization of the used models, e.g., which level of complexity the model has; (2) the way the model can be integrated into instruction, e.g., how the model is introduced to students; and (3) the way the model is used to foster scientific reasoning with focusing demands of German NES, e.g., if and how the model was critically reflected during the model use (detailed description of conceptualization of ELMO see 47 and 2.2.2). Aspects of ELMO can be used for describing model use in videos as well as live observations and measured quantitatively using a coding scheme [47
Previous studies only investigated teachers’ knowledge about models and modeling, and the effects of using a model on students’ achievement. There were hardly any studies that combined these three aspects: teachers’ professional knowledge, instructional quality features, and students’ achievement [58
]. In particular, there were no studies on facets of PCK including the use of models, one of the teaching strategies of science (for an overview, see [59
]). So far, results of several studies have not shown any effect of PCK on several instructional quality features as well as on students’ learning (e.g., [60
]). Using models in instruction as one of these instructional quality features is not taken into account for science teachers’ PCK.
1.4. Research Questions and Hypotheses
One main goal this study was to identify which subject-specific dimension of teachers’ knowledge (PCK or CK) leads to elaborate model use and, therefore, higher students’ achievement. Previous studies indicated that teachers’ knowledge about models and modeling in science is limited and divergent (e.g., [16
]). As teachers’ knowledge greatly influences instruction and assessment practice [46
], the effects of teachers’ different knowledge dimensions on teaching practice should be analyzed. Additionally, we hardly know what effective use of models in instruction looks like as previous studies only compared using models with other teaching materials and identified effects on students’ learning [17
Addressing these research gaps, we conducted a mixed-methods study with an explanatory sequential design [21
]. In the quantitative phase of our study, we analyzed the effects of teachers’ PCK and CK on students’ achievement mediated by their specific model use. In our study, this specific model use is represented by ELMO. An elaborate understanding of models provided by this way of teaching may facilitate students’ learning of content [54
], thereby leading them to higher achievement. Therefore, our research questions were:
In which way should models be used in biology instruction to achieve higher students’ achievement in biology?
Which dimensions of professional knowledge do teachers need for using models in a way leading to an increase in students’ knowledge in biology?
Based on our research questions and theoretical aspects, we formulated the following hypotheses for the quantitative phase of our study:
Hypothesis 1 (H1).
PCK and CK do not have a direct effect on students’ achievement.
Hypothesis 2 (H2).
PCK has an indirect effect on students’ achievement mediated by elaborate model use; CK does not show an indirect effect.
Teachers’ professional knowledge was measured using paper-pencil tests. Their instruction was measured by videotaping biology lessons, which were analyzed through a theoretically devised coding scheme focusing on ELMO.
Additionally, we were interested in a qualitative description of the application of ELMO in biology instruction. Therefore, we formulated an additional research question:
How can an effective model use in biology instruction be described?
Therefore, in the qualitative phase of our study, we described elaborate model use in biology instruction by comparing the extreme cases encountered by teachers. With these results, elaborate model use with examples can be understood in a better way by researchers, preservice and in-service biology teachers. In choosing a mix-methods approach, our assumption was “that the uses of both quantitative and qualitative methods, in combination, provide a better understanding of the research problem and question than either method by itself” [21
] (p. 535).