Assessment is today´s means of modifying tomorrow´s instruction. — Carol Ann Tomlinson

In my experience, students enter the classroom with a remarkable set of preconceptions about how science works in the real world. For this reason, I always first seek to understand each student’s mental model before attempting to teach a new concept. This strategy helps the student to recognize their beliefs early on in the lesson. The trick to understanding the student’s invisible model is to listen as they describe how it functions. Bringing their mental model out of their heads and making it shareable and physical is a part of the process for the student to recognize how they believe the world works.

Modeling is critical in a chemistry class, because students need to be able to generate both models and supporting scientific explanations of those models’ components. As their mental model becomes shareable, it takes the form of a physical model, which can be structural, behavioral, or functional in nature. Models can be developed as diagrams or drawings, replicas, analogies, mathematical equations, paper sliding, games, or simulations. The end goal is that students will use their model to determine whether their scientific explanation is accurate and uses data and evidence to explain the phenomenon, or needs further questioning and experimentation.

The challenging part for teachers and students alike is measuring their progress in changing their thinking. I try to be flexible when I am creating a set of bulleted requirements for their model and explanation. I have noticed that students do not all develop the same concepts at the same time, which means that I need to allow them opportunities to revise their model as their understanding deepens. I’ve also realized that letting students help me to create a loose set of requirements, and revise them periodically throughout the unit, really helps me differentiate my teaching approach in order to meet my students’ needs. Using a student’s model to assess their individual progress requires careful listening, rubrics listing specific components of the model, and students frequently evaluating themselves.

Figure 1. A student example of a Level 1 model. Click image to enlarge.

Levels of modeling

There are three levels of models used in the classroom, and all of them have value at different times, depending on where in the lesson sequence the modeling cycles will occur.¹ Authors Justi and Gilbert² elaborate on this view, observing that “… [students at] level 1 thought of models either as toys or as copies of reality. These sometimes have aspects or parts of the real thing omitted and are produced just to provide copies of objects or actions.”

Figure 1 shows a drawing of a level 1 model by my student — I’ll call her Sara — indicating that one substance was cold and another was hot. After she drew this model, I had follow-up conversations, both with Sara individually and as a class. As we talked about Sara’s model, she mentioned heat transfer, and following some discussion, she explained that energy was heat. I asked her how energy could be measured, and she decided that she would like to learn more about kilojoules as her next step for the model. Since this was Sara’s initial model, I was really listening for her foundational understanding, and also for any misconceptions. I wanted to hear her explain her thinking, find out if she knew whether anything was missing from her model, and ask her how she might be able to represent new ideas that came up in our conversation.

Figure 2. A student example of a level 2 model. Click image to enlarge.

According to Justi and Gilbert, “students in level 2 thought of models as being created for a purpose. The emphasis on some components is therefore altered, but the template of reality still predominates. The model is tested solely in terms of its fitness for the predetermined purpose.”

Once Sara realized that we could measure energy, I encouraged her to think about the differences between heat transfer in exothermic and endothermic reactions. In Figure 2, her revised model makes it clear that she has made progress and now understands the differences between the two types of reactions, but still lacks exact numbers. Consequently, we still need to focus on some of the components, like additional examples of chemical equations with the amounts of energy involved.

Justi and Gilbert note that “a level 3 understanding was found to have three components: a realization that a model is created to test ideas, rather than as a copy of reality; an acceptance that the modeler has an active role in its construction for a specified purpose; and the view that models can be tested and changed in order to inform the development of ideas.” When my students are ready to test their ideas, either with a hands-on lab or virtually, the modeling cycle is critical to capturing any new changes in their thinking. In my class, we use the simulation Reactions and Rates from PhET interactive simulations to see if there are additional components of heat transfer and types of reactions that we should learn about.

My objective is that the students will complete each stage of modeling. Throughout each of the stages, I assist students in developing and redeveloping their ideas by collecting data for their scientific explanation. Their data may come from labs, diagrams, hands-on activities, simulations, demonstrations, case studies, or research. As their model improves, we use the data to discuss the scientific concepts that the students are identifying. We write a lot at each modeling level and the students have to use data to make their claim evidence-based and reasonable.

Assessment of student understanding

In the above examples, I can use the various levels to determine students’ understanding of the scientific concept. For example, in level 1 activities, I look for an idea that is copied, but may still be missing some critical components of the concept. In level 2 activities, I look for a mostly accurate model with a purpose for the model and a significant scientific explanation. For level 3 activities, I look for an accurate model and an argument about a chemical phenomenon that could be tested. There are some limitations to modeling, and this is a great opportunity for students, especially those at level 3, to challenge their thinking about how to not only represent the abstract with a visual, but also how to develop a testable hypothesis to prove their ideas.

Getting started with modeling

It is very challenging to get students comfortable enough to share their thinking about scientific concepts, so I start with modeling on the first day of class. We draw a model of the scientific method, and during the first week students can add to it any new details that they learn, such as safety precautions or graph analysis methods. I draw my own model of each topic we explore, and I show students my progress on my model as we cover new topics. Whenever I ask students to do a revision, I show them my example first and explain why I added a concept, and how I represented it. Sometimes I start my model over completely, while other times I just tape another page next to my current model. In some instances, I just add a little drawing or word; this helps students to see that models can change and are flexible.

We use modeling cycles and rubrics in my class to track the changes and revise our models as we learn new concepts. Students can use a rubric as shown in Table 1, and can work in the classroom on developing a better understanding of one aspect of the rubric. We simply check off whether or not the required component was there; the student then knows what they still need to learn about in order to address it in their model in the next revision cycle.

There can be as many revision cycles as needed. However, I prefer to bring out the rubric every other week, because I like the students to get excited about its novelty in the classroom. Figure 3 is an example that I created to show a simplified version of model development and assessment.

We begin with a phenomenon, such as a video, demonstration, or photo; students then draw and label their initial model to explain how that phenomenon functions. For example, I asked one of my students to yell at my coffee and see how long it would take to heat it up to 75° F. She yelled into the coffee and we checked out a mathematical model of how long we would have to yell at the coffee to get it to be hot. I wanted students to think about how potential energy was turned into kinetic energy, so that they could understand that the human voice carries energy and identify that energy is heat. We also mixed a highly viscous liquid and measured the temperature before and after, and put Epsom salts in water and measured the temperature before and after. I asked the students to draw a picture of how they imagine substances get hot or cold (resulting in the student model shown as Figure 1).

After students observe the phenomenon, we write a list of questions that we want to learn more about and then share our questions with each other. Students rate the questions in order of importance, and change any close-ended questions to open-ended. We then make a list of items we want to study and include on the rubric. During this time, I can add important concepts as well.

I provide students with a rubric for the level 1 components that we have determined they need to know to be able to understand the concept. I differentiate between vocabulary introduced from the rubric and from the students’ inquiry questions, because every student ́s model will be different. I listen closely as students describe their models and identify which specific models will help us drive the storyline and argument of the chemistry concept involved. I also look for misconceptions that may need remediation before the student will be able to make progress.

Formative and summative assessment

Assessment of models can be either formative or summative. Sometimes I will ask for a quick diagram or drawing that is meant to see what students already know and are capable of. I will not grade these diagrams, but rather analyze them to see how the students are doing and what they need to learn next. Sometimes we will have studied a concept for several weeks, and the students need to apply their learning about the concept by testing the model within a simulation. In this case, I grade their answers to each of the components that they tested. After the simulations, I may also have them do a self-reflection of their progress, and only grade that.

My decision to grade a model or not depends on a few factors, including whether or not students:

• had time to revise their ideas and collaborate on their models,
• have worked through the major vocabulary, and
• have told me that they are feeling confident with the material.

Students frequently do self-evaluation of their models to develop metacognition about their own mental and physical models. After students understand the limitations of their models, they can complete a revision.

As students are working through their model revisions, I provide additional experiences that will move their understanding forward. Typically, this involves sharing a data set for students to analyze, either one that I give to them or data that they collect themselves. Students use this data to develop their scientific explanation about the concept. For example, to answer such questions as, Why is the honey/simple syrup heating up from mixing? Is this a physical or chemical change?, students collect temperature data before and after mixing.

There can even be models within larger models. When students are studying different types of chemical reactions, they have to draw a picture of how they think each type of chemical reaction works. Afterward, I give students a handout with different chemical reactions labelled as endothermic or exothermic. The students then must decide whether they are missing any information from that handout on their models. If they are, they can add the information to their model and check it off on the rubric. Students can then use a kit like Happy Atoms to see the types of bonds that are occurring within the reaction.

The first year that we used manipulatives to model bonding, we made models of all the elements on the periodic table using Styrofoam balls and pipe cleaners to represent the bonding electrons and lone pairs. This is an example of a model revision and a model within a larger model. Students may decide to test their ideas about bonds, energy, and types of reactions at this point. They could create a model that represents the state of molecules in the lab before, during, and after the experiment. Students are always welcome to return to the model and add information gleaned from the learning activities.

Students who have mastered the level 1 model are encouraged to develop a revised, more accurate model with an evidence-based scientific explanation presented verbally or in writing; this is an important part of the modeling cycle, because the students need to be able to revise and expand their ideas. The teacher can help the students to make such revisions by providing opportunities to collect data either through experimentation or research. The physical model helps the student to support their reasoning in the scientific explanation.

Lessons learned

Modeling began in my classroom unknowingly. I knew that I needed to model and so I did that frequently. After taking an online professional development class from National Geographic, I discovered that by having students do drawings and simulations, I was allowing them to model. However, this approach was lacking: first, in its ability to help me monitor and assess progress, and second, in its ability to help students improve how they used evidence to explain their scientific thinking verbally or in writing. Once I developed more insight about my ability to track the changes in the students’ thinking, I also found more purpose within the lesson, and was better able to identify experiences to help my students build an argument using evidence, create their own model, and eventually test their underlying ideas.

It is important that we guide our chemistry students through inquiry, identifying which models chemists currently accept, as well as the models’ limitations. By teaching our students to constantly question their beliefs and assess their own understanding, as well as providing them the tools and a basic outline of what questions they need to address in their thinking, we can teach them to be real scientists: testing their ideas and modifying their mental and physical models as their ideas change.

References

1. Grosslight, L.; Unger, C.; Jay, E.; Smith, C. Understanding models and their use in science: Conceptions of middle and high school students and experts. Journal of Research in Science Teaching. 1991, 28, no. 9, 799–822. https://doi.org/10.1002/tea.3660280907
2. Justi, R.; Gilbert, J. (2003). Models and Modelling in Chemical Education. In Chemical Education: Towards Research-based Practice; Gilbert, J., De Jong, O., Justi, R., Treagust, D., and Van Driel, J., Eds.; Springer: Dordrecht, Netherlands, 2003. 10.1007/0-306-47977-X_3.

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