Abstract
Existing instructional materials for chemistry offer a huge range of different external representations that can be used by chemistry teachers to support students’ understanding of chemical concepts like the concept structure of matter. In science, different kinds of representations are usually combined forming multiple external representations. Examples are combinations of texts, pictures, figures, diagrams, graphs, tables, schemes etc. However, these multiple external representations often have problematic features and/or do not meet students’ subject-related learning needs. For example, many external representations do not take different representational levels into account and/or mix information on the macroscopic level with those from the submicroscopic level. Such representations have the potential to favor students’ misconceptions who often struggle with separating different representational levels. Therefore, it is important to highlight crucial characteristics of external representations that potentially facilitate students’ learning of chemical concepts at lower secondary schools (age group 10–14). When chemistry teachers consider and reflect crucial characteristics of representations and adapt existing external representations or develop new ones, these new representations can become powerful cognitive tools helping to make instruction in chemistry more effective and coherent. This article answers the question What makes representations good representations in science education? by describing features of effective learning with decisive characteristics of multiple external representations and highlighting these characteristics by means of concrete examples from chemistry learning. Finally, an online tool will be outlined that can help teachers to improve multiple external representations for use in chemistry classes.
1 Introduction
Learning in chemistry education starts with recognizing and describing chemical phenomena. Students from lower secondary classes have already observed or experienced such phenomena in their everyday life, consciously or unconsciously. For example, most students from that level know that objects can sink or float; they have seen how substances change their aggregate state. However, they are often not able to explain how and why these phenomena happen and why there are differences between different substances (Smolleck & Hershberger, 2011; Unal, 2008). To be able to do this, students need models that help to explain chemical phenomena through abstraction, like a simple particle model. To introduce such models, chemistry teachers typically use multiple external representations (MER). Such an MER can be a combination of a written text that explains a phenomenon and a graphical representation that offers a possible model as well as a combination of two different pictures. Since students often struggle with MER (e.g. Cromley et al., 2010), the use and design of MER requires the observance of certain rules. MERs of poor quality can inhibit students’ learning progress and can also cause misconceptions. The following article summarizes seminal empirical findings from cognitive psychology and science education that are relevant for using MER in chemistry classes. Based on this, criteria are presented that can help teachers to consider decisive principles of designing or adapting MERs. The principles will be explained based on existing examples of MER that have desirable and undesirable features. Finally, an outline of a developed online tool will be given that has the potential to facilitate the reflection of MERs’ quality.
2 MERs’ general characteristics – an overview
In the disciplines of science, it is common to combine different types of external representations (ERs; Tsui & Treagust, 2013), for example texts and pictures. They result as MERs and are highly prevalent in chemistry. In order to be able to describe learning with MERs, theoretical basics from the perspective of cognitive psychology are summarized in the following.
According to their characteristics, ER can be classified in different ways. Widely used and particularly relevant from a cognitive psychology perspective is the distinction between depictive (pictorial) and descriptive (textual) representations (Schnotz, 2002). Descriptive representations consist of symbols characterized by an arbitrary structure. Appropriate conventions determine which object a symbol represents. Typical examples are texts and mathematical equations. In contrast, depictive representations consist of iconic signs. Whereas realistic pictures (e.g. photographs, drawings) are similar to the represented object, logical pictures (e.g. graphs, diagrams) are more abstract. Combinations of two or more individual representations are called MERs.
When trying to understand the information in an MER, individuals construct an internal mental model in their cognitive system. According to the integrated model of text and picture comprehension (Schnotz, 2014; Schnotz & Bannert, 2003), a sensory register conveys the information of external representations (i.e., texts and pictures) to the working memory. Here, text is first processed in a descriptive subsystem and then in a depictive one; the opposite is assumed to apply to pictures. Individuals also integrate prior knowledge stored in their long-term memory when constructing an internal mental model (Schnotz, 2014).
According to Mayer’s multimedia principles, an MER constituted by text and picture promotes better comprehension than text-only learning material (Mayer, 2001). This is in line with Paivio’s dual coding theory which also assumes two different cognitive subsystems for verbal information such as texts on the one hand, and nonverbal information such as depictive representations on the other (Paivio, 1986). As an important benefit of MERs, complementary information could be conveyed by more than one individual representation in cases where inserting all information in one single representation would be too complicated (Ainsworth, 2006). Empirically, undergraduate students’ working with text-picture combinations outperformed students that worked only with textual material (Eilam & Poyas, 2008). However, not every depictive representation added to the text helps identifying and processing information. For instance, it is assumed that task-inappropriate types of depictive representations may interfere with constructing a task-appropriate internal mental model (Schnotz & Bannert, 2003).
Learning theories that build on the cognitive psychological theories of processing texts and pictures elaborate on learning with MERs (e.g. Ainsworth, 2006; Seufert, 2003). Basically, when MERs are used, students are required to understand each of the representations by itself. Further, they have to disentangle which aspects of a conceptual framework are represented in such an external representation. Then, they have to understand the meaning of the relations between more than one representation. By analyzing these relations, students interpret similarities and differences of corresponding elements and structures of two or more representations aiming at coherence formation. Besides, students infer information from different representations when learning with MER that are related to the underlying science concept (Schnotz & Bannert, 2003). For example, when students learn with MER that encompass verbal and pictorial representations like texts and diagrams, they have to decode the presented information and relate them to each other.
3 The role of MERs in science learning – a summary
Successful science learning requires developing an understanding of scientific concepts and their communication. This understanding is characterized by three aspects: students must (1) have a sufficient base of factual knowledge, (2) understand the respective facts and ideas in the context of a conceptual framework, and (3) organize their knowledge in ways that facilitate retrieval and application (Bransford et al., 2000). MERs can be seen as a key to achieve this conceptual understanding of science concepts as they function as cognitive tools (Rappoport & Ashkenazi, 2008; Schnotz & Bannert, 2003; Seufert, 2003).
When developing an understanding of science concepts, from a subject-related perspective it is necessary to distinguish between different levels of abstraction. According to this distinction, the macroscopic or phenomenological type, the submicroscopic or model type, and the symbolic type can be distinguished from each other (Gilbert & Treagust, 2009). This classification goes back to Johnstone (1982) and has been reinterpreted and adapted several times (e.g. Talanquer, 2011). An MER in this sense could be, for example, the combination of two pictures in two different levels: a photo of a cut diamond (macroscopic level) and a picture of the crystal lattice from carbon atoms (submicroscopic level).
Specifically for chemistry education, Kozma and Russell (1997) concluded implications for curricula and instruction based on their research on learning with MER. For example, students should be able to identify and analyze elements and structures of a particular representation as well as patterns in them, to convert one type of representation into another as well as to map elements and structures of one representation onto those of another, or to generate or select an appropriate representation or MER to explain chemical phenomena or concepts. The assumption is that students develop an understanding of science concepts when actively working on and with MER in the described way and when also linking phenomena, science concepts, and representations of both (Seufert & Brünken, 2006; Waldrip et al., 2010; Yore & Hand, 2010).
Results of empirical studies show that students often have difficulties when learning with MER in science. Authors showed that challenges solving science tasks with MER even persist beyond secondary school. One of these difficulties is that students often only notice elements or structures on the surface level of a representation like symbols, colors, or lines (Bodner & Domin, 2000) instead of using the underlying information as evidence to support claims or to explain, draw inferences, and make predictions about relationships among chemical phenomena or concepts. Moreover, it appears that students do not fully use pictures’ potential. For example, Cromley et al. (2010) showed that undergraduate students working with texts and pictures dealing with science topics often just skimmed or skipped the pictures. But students who sufficiently focused on pictures employed a higher proportion of high-level cognitive activities (Cromley et al., 2010). Not paying sufficient attention to pictures will be particularly problematic when the depictive information is not repeated in the text; no adequate mental model can be constructed due to the lack of depictive information.
Therefore, it is not only necessary that students are actively engaged in working with representations in chemistry classes, but also to foster students’ representational competence by explicitly engaging students in the creation of various forms of representation and in reflection on their meaning (Kozma & Russell, 1997, 2005). Students should be encouraged to represent chemical phenomena and concepts in a variety of ways. Also, teachers’ use of representations in the classroom can have a significant impact on students’ (representational) understanding (e.g., Leopold et al., 2013; Rau, 2018). However, not much is known about the exact use of representations in class (Nitz et al., 2014) and in learning material like school books (e.g. Wernecke et al., 2016).
Not surprisingly, MER cannot only support or facilitate learning, but also inhibit or complicate student learning. For example, poor structured representations can have a negative effect on student understanding of science concepts. This means that e.g., conceptual change is not supported by representations but even inhibited (Ainsworth, 1999, 2006). Another often cited problem is that within representations different levels of representations are mixed up so that students do not know if presented information are true for the macroscopic or the submicroscopic level (Gilbert & Treagust, 2009).
4 Quality criteria for MERs – a rubric as a guide
When looking at the quality of MERs, a large variety of possible criteria can be considered that are grounded in the research fields of cognitive psychology and science education (e.g., Gilbert & Treagust, 2009; Mayer, 2014; Tsui & Treagust, 2013). While cognitive psychology mainly focuses on general (design) aspects that should facilitate the information processing (Ainsworth, 2006; Mayer, 2001), science education predominately focuses on content aspects – in chemistry, first and foremost, on the relation of the macroscopic, symbolic, and submicroscopic level used for describing and explaining chemistry subject matter (Talanquer, 2011). Some very basic elements and structures of MERs were condensed to a self-assessment rubric for in-service teacher candidates.[1] The text below follows the structure and content of the rubric that addresses five main categories. Each main category includes several criteria that can be used to rate worksheets for chemistry classes on a 5-point Likert-scale. After having presented the rubric in general, its’ central criteria will be explained in Section 4 by using sample worksheets.
4.1 Category 1: alignment with the learning objective and learning group
The first category addresses general aspects of learning materials to get a first impression of their quality and to check if the instructional material fits the learning situation at all (Table 1). The instructional material should be concise so that learners can focus on the actual content and are not distracted by irrelevant information (Harp & Mayer, 1998). Thus, in the first step, it is important to specify which specific chemical contents belong on the worksheet and which do not. If, for example, the learning objective is the introduction of the particle model, then the worksheet may only contain information that refers to this topic. Topics that go beyond the learning objective, as states of matter or mixtures of substances, or just seem to be interesting, may not yet be covered in this worksheet. Once the relevant content has been identified, the next step is to consider how the information is distributed between text and pictures and how both types of representations are designed.
Quality criteria concerning the alignment of MER with the learning objective and learning group.
| 1. The entire content of the material and the amount of information within the material are adequate to achieve the learning objective. |
| 2. The entire content of the material and the amount of information within the material are adequate for the grade level as well as for students’ abilities and needs. |
| 3. The MER only contains information that is relevant to the learning objective – no more and no less. |
| 4. Decorative pictures or symbols are avoided because they tend to distract during the learning process. |
| 5. The content of the entire MER is consistent and coherent, just as it is between the text and pictures. |
| 6. The text of the MER refers to science concepts and theories (theoretical part) whereas the pictures show a concrete example (practical part). |
| 7. The heading fits the content of the MER and is formulated in an interesting way. |
4.2 Category 2: the pictorial representations’ design
Apart from looking at the whole MER, it is necessary to look at the different parts of it separately as individual representations. In this manner, Category 2 helps to analyze pictorial representations (Table 2). The pictorial part of an MER is considered first, because from a science teacher’s point of view, pictures are technically more difficult to edit, correct or redesign. So, if the pictorial part is revised as well as possible, it is easier to adapt the text to the picture than to do the process in reverse order.
First, the picture types should be identified to check whether their characteristic properties have also been implemented correctly. For example, there are defined conventions for diagrams used in chemistry with coordinate systems that must be adhered to. Other considerations include, for example, pictures in which molecules are represented in the particle model as spheres. Can a water molecule be illustrated in blue or a sulfur molecule in yellow color? How are colors and size ratios matched? Where are elements in the picture that can evoke misconceptions in students? How can these aspects be corrected? These and similar criteria should be considered when editing or designing a picture.
Next, the pictures’ suitability and design should be assessed in detail (e.g., Harp & Mayer, 1998; Mayer, 2014; Weidenmann, 1988). Especially considering the representational levels, it is also necessary to analyze the position of the elements within a pictorial representation (Mayer, 2014; Tan et al., 2009). Elements of a picture or drawing that belong to the same level (e.g., sugar particles and water particles on the submicroscopic level) should be spatially close; those that do not belong together should be spatially separated (e.g., a sugar cube on the macroscopic level vs. a sugar particle on the submicroscopic level). Another aspect to consider is highlighting elements in a picture. Highlighting can help the reader to understand the picture better by recognizing the most important features (Mayer, 2001).
Quality criteria for MER concerning how to design pictures.
| 1. Which type of pictures are in the MER? (realistic picture, schematic picture, logical picture/figure, science specific diagram) |
| 2. The used types of pictures are adequate for the learning objective and students’ abilities. |
| 3. The most important elements of a picture are made salient by highlighting (e.g., arrows, different colors, labeling, numbers, etc.) |
| 4. If there are captions in or under the pictures, they are short and concise and clearly refer to the relevant element by inserting lines, dashes, arrows, numbers, etc. |
| 5. Elements of a picture that belong in the same representational level are spatially close while elements from different levels are separated. |
| 6. The size of the picture is appropriate – not too small and not too big. |
4.3 Category 3: the verbal representations’ design
Like pictorial representations, verbal representations can also be classified into different categories and types. First, verbal representations are divided into main and additional text and then into subtext types. The main text provides all textual content that is necessary for achieving the learning objective while the additional text can be added optionally as summaries, extra information, and tasks to facilitate the main text’s comprehensibility (Ballstaedt, 1997).
When the characteristics of the main and additional texts are clear, it is important to find a suitable introduction to the chemistry topic for the students (Table 3). This should ideally be achieved with a context that raises a problem, an issue, or a task and that relates to the students’ everyday life or experience (Bennett et al., 2006). A possible problem for the introduction of the particle model could be: Why can you no longer see the sugar in the tea, but still taste it?
Next, the text is analyzed on the paragraph, sentence, and word level. The information should be in the right – that means logical and chronological – order. The chemical language and the linguistic level should be optimized. Every single word in the text should be used thoughtfully, be precise and unambiguous, and give no room for misunderstandings. (Example: Water molecules look like tiny colorless spheres. Correction: We can imagine water molecules like tiny colorless spheres.) Likewise, it is very important to define technical terms when they are first used and to always use them consistently. If important key terms are typographically highlighted, the most important information can be taken from the first skim (Ballstaedt, 1997).
A small reformatting in the text can simplify the sensory reception and cognitive processing of the text: When reading, the eyes jump from word fragment to word fragment in small irregular intervals. The simpler the font style is and the narrower the text width, the easier is the sensory reading process. Therefore, it is suitable to divide the main text into columns (comparable to newspaper articles) and to limit the number of words within a line to 5–7 words (Ballstaedt, 1997).
Quality criteria for MER concerning how to design texts.
| 1. Which type of main text is used in the instructional material? (narrative, descriptive, explicative, instructive, argumentative, etc.) |
| 2. Which types of additional texts are in the instructional material? (introduction, tasks, information about the learning objective, summary of the main text, excursus, etc.) |
| 3. The used types of main and additional texts are adequate for the learning objective and students’ abilities. |
| 4. The text begins with a context as an introduction for the topic. |
| 5. The context contains all didactic criteria of contexts. (definition of a problem/issue/task, relation to students’ the everyday life/experience) |
| 6. The subject matter is first delivered as a whole and then in detail. |
| 7. The whole text has a clear common thread. |
| 8. The text is visually structured by paragraphs that make sense in terms of content. Different types of texts are also clearly distinguished from each other, e.g., by paragraphs or frames. |
| 9. Headings and key terms are typographically highlighted. (bold, italic, colored, underlined, framed, etc.) |
| 10. The chemical content described in the text is chemically correct. |
| 11. The chemical language and the linguistic level in the text (terms, sentences, grammar, length) is appropriate for the grade level and students’ abilities. |
| 12. Chemical terms are consistent. Synonyms are not used for (chemical) terms. |
| 13. The text’s font is kept simple. (uncolored and simple font type, pleasantly legible font size and line spacing, white text background) |
| 14. The text contains as few word separations as possible. The line width should be limited to 5–7 words. |
4.4 Category 4: quality criteria for the MER’s design
After the representations have been adapted and optimized individually, the next step is to assemble and form them to an MER (Table 4). At first, and similar to the text’s categorization, it should be clear which of two or more representations (text or picture) is the main and which is the additional representation. The main representation provides the most important information to achieve the learning goal. The additional representation either presents the same information in a different form (complementary function) or provides additional information for single aspects (constrain interpretation or construct deeper understanding). However, some MERs are designed to contain non-redundant information. In this case, the relevant information (e.g., a conclusion) is obtained by combining both representations (Ainsworth, 1999). Next, it is important to reflect if every individual representation is chosen and designed correctly concerning their type, function, placement and linking with the other representations. Still referring to the example with the introduction of the particle model, it is indispensable to use a description (text) with a visualization (picture) of this model. In contrast, it does not make sense here to show a water molecule as a structural formula (a mathematical or chemical formula is also considered to be a picture.).
For the science educational perspective, it is especially important to analyze the representational levels in the MER and the relation between them. Basically, the following four levels have to be differentiated in representations: the macroscopic (e.g., a sugar cube), microscopic (e.g., a sugar crystal), submicroscopic (e.g., a sugar molecule in the particle model), and symbolic level (e.g., the structural formula of a sugar molecule). On the one hand, the levels have to be separated verbally AND visually (verbally e.g., a sugar molecule cannot melt, but a sugar crystal can; visually e.g., a sugar molecule cannot be shown in a beaker, but a sugar crystal can). On the other hand, there should be explicit links between the levels that explain their relationship (e.g., Gilbert & Treagust, 2009; Kozma & Russell, 1997; Tsui & Treagust, 2013).
Quality criteria for MER and the representational levels.
| 1. Which element of the MER is or are the main representation(s)? (text and/or picture) |
| 2. Is there an additional representation and which representation is it? |
| 3. What is the relationship between the main and additional representations? (complementary roles, constrain interpretation, construct deeper understanding) |
| 4. If the main and additional representations are placed horizontally next to each other, the main representation is on the left side. OR: If the representations are positioned vertically one below the other, the main representation is at the top. |
| 5. Additional and associated texts and pictures are positioned spatially close. |
| 6. Cross-references in the text directly refer to concrete elements in the pictures. |
| 7. The chosen representational levels are appropriate for the learning objective. |
| 8. The levels are clearly separated in all individual representations – visual and verbal. |
| 9. The levels shown in the pictures are linked with each other. |
| 10. The levels described in the text are linked with each other. |
| 11. The chosen levels do not raise students’ misconceptions. |
| 12. It is made clear that chemical representations and models are possibilities for explanations to understand the submicroscopic reality. |
4.5 Category 5: quality criteria for tasks
To engage students with the learning material and to foster students’ interaction with the MER, carefully and in detail developed tasks must be used (e.g., Leisen, 1998). On the one hand, tasks must be clearly understandable and transparently specify the scope of the expected solution. On the other hand, they must address all the contents of the instructional material so that learners actively work with the material (Table 5).
Quality criteria for MER on how to formulate tasks.
| 1. The tasks are formulated as precise instructions by verbs/imperatives. |
| 2. The tasks aim at a constructed product from the students. (e.g., a summary, description, explanation, diagram, chart, calculation, formula, chemical equation) |
| 3. The tasks address different difficulty levels. |
| 4. The tasks make the students work with each representation or element to a high degree. |
| 5. In one of the tasks, students are asked to gather information from several different representations into one answer. |
| 6. In one of the tasks, students are asked to transfer the content from the text and/or picture into a new representation type that does not exist in the MER. |
5 Evaluating and designing an exemplary MER
To explain the quality criteria listed in Section 3 in more detail and with examples, it is shown how such a process of designing instructional material might look like and how the rubric can support that process. As an example, there is a finalized material (Figure 2) which was designed by a chemistry teacher candidate within the project. As a starting point, the in-service teacher candidates received a common learning objective as well as ready-to-redesign visual and verbal ERs (Figure 1).
Four variations of visualizing the process of dissolving sugar in water (authors’ translation from German to English).
Exemplary instructional material designed by an in-service teacher candidate (authors’ translation from German to English).
The chosen chemical topic is typical for chemistry in lower secondary schools. It can be used to introduce the concept substances and substance properties. The learning objective or the students’ competence to be promoted by the instructional material is: The students are able to describe the structure of substances and matter using the example of the spherical particle model.
To start, the teacher candidates receive a collection of different pictures referring to the same topic (Figure 1). All four pictures from the example are intended to show how to imagine sugar dissolving in water according to the particle model. A beaker is shown as a vessel, sugar as a substance to be dissolved, and water as solvent. The pictures differ from each other in partly small details, which can, however, have a great influence on students’ learning process.
Now, which picture has a higher quality and is more suitable for the use in a worksheet? Considering the rubric, a viewer who looks at the pictures from A to D could notice the following things:
Pictures A and B are similar and differ from the Pictures C and D by the separate visualization of the molecules in a zooming circle. Both pictures also present more information than C and D. In Picture A on the left-hand side of the picture, there is a beaker filled with water and two sugar cubes. On the right-hand side, there is an enlarged section of the beaker showing the dissolution process on the submicroscopic level. The sugar particles are drawn in dark gray color and the water particles in light gray. The water particles are much smaller than the sugar particles. Further, the water particles are arranged irregularly and the sugar particles regularly. Both substances are labeled on both levels (sugar cube/sugar particles, water/water particles)
The second picture B is similar to A, but with a less strict visual separation of the macroscopic and submicroscopic level. The labels for the substances and its particles are written next to each other (sugar cube/sugar particles). Analyzing the colors, the sugar particles are white with a black outline contour and the water particles are light blue with a dark blue outline contour. The background color of the water molecules is light blue like the color of the water molecules themselves. Because the molecules have the same colors as their background, it appears to the viewer as if molecules were empty matter through which one can see. In addition, the blue background makes it seem as if the space between the water molecules is also filled with water. This can lead to the misconception that water molecules are swimming in water.
The next pictures are a little different than the first two. On the one hand, the beaker is shown on the macroscopic level; on the other hand, the substances sugar and water are shown on the submicroscopic level within the beaker. Only the elements of the macroscopic level are labeled. The sugar particles are shown in white color and the water particles in dark blue color with a light blue background. The first sugar particles between the water particles indicate the beginning of the dissolution process. The sugar particles are much smaller than the water particles. Besides, both types of particles (solid and liquid) are arranged regularly in lines. Here, too, there is a risk that the possible misconceptions as in picture B can be evoked. In addition, the levels are mixed too much so that students cannot separate them. The size dimensions are also mixed. Relative to the size of the beaker, the molecules are shown too large, i.e., they should be extremely small and not visible. Besides, the sugar molecules appear to be smaller than water molecules.
In the fourth picture, the water as substance is drawn in another way than in Picture C. The water particles have no color and just a blue outline contour. When looking at the picture, it seems as if the water particles are within a liquid of blue color. Both types of particles are still arranged regularly. Labels are missing.
According to the above summarized theories, research findings and the rubric, it quickly becomes clear which picture is the most accurate variant and which pictures need more or less improvement before classroom use. The first picture is the most appropriate of the four examples, because the representation is clearly divided into two sections: one displaying the dissolution process on the macroscopic and thus the visible level, and another one displaying the process on the submicroscopic level and thus the not visible level. The colors and the proportions of the individual elements are also appropriately chosen, so that no or as few misconceptions as possible should arise.
In addition to the displayed pictures, the chosen Picture A could be combined with a text in order to design an instructional material. Figure 2 shows a possible text consisting of four different sections and text types. In alignment with the rubric, the text starts with a context for the dissolution process that can help students to relate science concepts to their everyday life. In this case, a situation from breakfast was chosen, in which tea is sweetened and the sugar is no longer visible. The second section is an explicative text that explains the underlying phenomenon behind the dissolution process. The particle model is introduced. The third section leads the learner to another, but also very important direction and is a descriptive text. It stimulates the learner to think about model criticism and criticism about the particle model. Finally, the last section summarizes as an additional text the most important information of the instructional material. This section is also framed and labeled with a symbol, so that the reader can directly identify the most important message of the instructional material.
With reference to the representational levels, the text attempts on the one hand to explain what happens to the sugar on the individual levels; macroscopically, the sugar can no longer be seen and submicroscopically, the sugar particles are distributed between the water particles. On the other hand, the model critique also describes how these two levels are related to each other; macroscopically the sugar is no longer visible and submicroscopically this phenomenon can be explained with a model. It is always necessary to refer on the one hand to the separation of the levels and on the other hand to the relationships between the levels, so that, if possible, no chemical misconceptions and confusions are evoked on the students’ side.
Looking at the relationship between both representations (text and picture) in the exemplary instructional material (Figure 2), the main representation is the text because the particle model is a more theoretical model. The picture of dissolving sugar is an additional representation with an example for the particle model that supports the understanding of the text. The model’s properties can be found in the picture but are not immediately obvious for a novice. So, the picture helps to constrain or guide the text’s interpretation.
The cross-references between text and picture are given once in terms of content and once in terms of form. The text does not only explain the particle model, but also refers directly to the example with sugar and water. The formal link is made literally and in color at the same time. First, the text refers directly to the picture with as in Figure 1. Secondly, the terms sugar and water are marked or underlined with colors both in text and picture, so that the reader can switch immediately between the text and the picture while reading.
Looking at the tasks in Figure 2, concrete imperatives or prompts were used. The expected amount of the answer (e.g., 5–7 sentences) is also specified. The difficulty level is increased from simply describing (task 1) to distinguishing (task 2) and from explaining (task 3) to presenting, transferring, and applying (task 4). In addition, a third and new type of representation is introduced in the second task. Here, students are asked to extract the information from text and picture and to translate it into the form of a table.
6 Summary based on existing experiences in chemistry teacher education
This article addressed the question: What makes representations good representations for science education? In general, the construction and development of MER is a difficult task for teachers as it is currently rarely a part of teacher education curricula (Hattie, 2009; McElvany et al., 2012; Nitz et al., 2014; Schroeder et al., 2011). Prospective science teachers need to acquire subject-specific knowledge about representations and their meaning in learning science concepts, as well as knowledge about subject-specific student prerequisites and teaching strategies (McElvany & Willems, 2012; Nitz et al., 2011). A study on teachers’ diagnostic competence in text-picture integration showed that teachers tend to overestimate material and tasks with texts and pictures in terms of difficulty, while they tend to underestimate learners’ abilities in this area (McElvany et al., 2012). One consequence of such misjudgments could be that learning materials with external representations are not optimally integrated into lessons (McElvany et al., 2012).
Within the project, the ERs and designed MER presented above were used for a training with chemistry in-service teacher candidates. The teacher candidates’ task was to notice problematic features within the ERs, to improve them according to the rubric and to combine them to an MER. In total, the in-service teacher candidates designed three different instructional materials and afterward applied the rubric to their self-designed material. Through the repeated use of the rubric, a significant positive change and a higher quality of the instructional material could be noted. In the first step, the teacher candidates improved general aspects such as the structure and typograph of the text. The separation of the representational levels in the pictorial and verbal ER was also implemented directly even if this criterium was identified as being challenging by teacher candidates (Bucat & Mocerino, 2009). In the second step, the teacher candidates concentrated more on content-related aspects such as the chemical language and formulation as well as more specific tasks. Besides, the more often they used the rubric, the more their perceived difficulty of working with the rubric decreased.
Showing imperfectly developed and improvable examples of ER and introducing a newly developed rubric, this article explained some improvement mechanisms that can help science teachers to increase the quality of instructional material. In this way, the article provided a teacher-oriented summary of some important findings on MER and a practical guide for transferring them to science classes. A next step in the development of the rubric could be the adaptation of the rubric to more interactive and dynamic materials that require other and/or further quality criteria as they also include audio and video material.
Funding source: Deutsche Forschungsgemeinschaft
Award Identifier / Grant number: RO 5243/2-1
Award Identifier / Grant number: SCHW 1866/2-1
Acknowledgments
The authors thank all in-service teacher candidates who participated in this study. They also thank the Ministry of Education of the State of North Rhine-Westphalia and the mentor teachers from the teacher training seminars who supported and facilitated the study implementation. Further, the authors thank the German Research Foundation for its financial support under grant RO 5243/2-1 and SCHW 1866/2-1.
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Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
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Research funding: None declared.
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Conflict of interest statement: The authors declare no conflicts of interest regarding this article.
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