II Creative Reasoning Processes to Support Model Evaluation

These are ways to support student reasoning while they are evaluating a model.

Evaluatory Observations

Recall evaluatory observations
Make a prediction and collect evaluatory observations
         (sometimes by having students contribute to the design of the experiment)
Use a demonstration and ask for evaluatory observations
         (no example provided for this common strategy)

Theory-Centered Strategies

Use Extreme cases
Evaluate on internal coherence
Run the model
Use Thought Experiments

A teacher can also directly ask students to evaluate the model.

Examples of each are given below.


Evaluatory Observations

This type of observation is conducted or recalled after students have their initial models. They can use those models to make predictions and then conduct or recall evaluatory observations to test those predictions.

(1) The class may recall an observation that conflicts with or supports the model
(2) Observations can be designed expressly to test student predictions.

A circuit diagram shows a single battery with two identical bulbs connected in series. Six lines radiate outward from each bulb, indicating that they are of equal brightness.Example 1: Recalling known observations conducted in the class

Students suggest that currents are different in different parts of an electric circuit.

The teacher asks them what the results were in a previous lab during which they had measured current as being the same in all parts of the circuit.

A cartoon diagram of a human head has been annotated by a student to show a tube leading from the nose down through the throat, and another tube leading from the mouth down through the throat. The two tubes do not connect.Example 2: Recalling known observations from life experience

Students were evaluating a student-drawn model of the throat that had one tube going from the nose to the lungs and a separate tube going from the mouth to the stomach. The teacher asked, “What evidence do we have? … Can you swallow and breathe at the same time?” Students replied, “No!” and, “You choke.”  

This was an evaluatory observation serving to expose a problem with their current model. (They decided that there must be a single pipe that somehow went to both the lungs and the stomach. Later, they decided that the pipe must start out as a single pipe and then have two branches. This episode continues in Example 8.)

Example 3: Recalling known observations from life experience

T: This model says that bulbs always light when a battery is present, but have you ever heard of a short circuit?

Hand drawing of what is essentially a single lung with a suggestion of two lobes. It has mostly hollow space inside with a hole at the top for air to get in and another hole at the bottom, presumably for the air to get out.Example 4: Recalling known observations from life experience

A student group draws a model of the lungs as one large cavity with 2 lobes, with no division between the lobes.

T: Have you ever heard of anybody having a lung taken out?

Example 5: Making a prediction, designing an experiment to collect evaluatory observations

After asking for opinions on whether we breathe out less than we breathe in because we absorb all the oxygen, a teacher asks, “Could we use the breath measuring tube to see if we exhale about as much air as we inhale?



Theory-Centered Strategies

In contrast to the data-centered (empirical) strategies above where students make observations to evaluate a model, the following are theory-centered (non-empirical) strategies where students evaluate a model for scientific criteria such as coherence or viability in a thought experiment.

Extreme Cases

During extreme case reasoning, discussion is about the effects of setting an extremely high or low value for some variable in the system. Considering what their model predicts if one aspect of the model produces an unusually small or large effect allows students to see whether their model still works for those cases.

Example 6: Using an Extreme Case

A middle school teacher asked her students, “What are sources of energy for our body?” The students suggested water, exercise, air, food, and sun among other things. These are common answers from students of this age. The teacher then suggested, ”Let’s examine whether you get energy from the air that you are breathing. How many times do we breathe in a minute?” She had the students count their breaths and they found that they took about 22 breaths per minute. Together, they calculated that a person could take about 32,000 breaths a day. The teacher then commented that a person could get a lot of energy and increase his weight a lot just by breathing. If a person obtained 100 calories in every gulp of air, after only one day that person would increase his weight by 1000 lbs. She asked the students if that is really what happens. “How much does a newborn baby weigh?” Students answered, ”Around 7 pounds.” The teacher pointed out that if the baby could get energy just from breathing, assuming a rate of 100 calories per breath, by the very next day he would weight 1000 pounds. “The baby would be so big that the parents could not hug him, and they would need a truck to carry the baby? Is that what really happens?” Students gave a resounding “No!” Laughing, they decided that, considering how much we breathe, it does not make sense that air is a source of energy for our body.

This Extreme Case is also an example of a Thought Experiment, described below.


Evaluate on Internal Coherence

In this kind of discussion, the teacher helps students consider the logic of their models to identify consistent or inconsistent (contradictory) features within the models.

A simple chalk drawing shows lungs and heart connected with a circulatory loop. One part of the loop goes from the lungs to the heart and is labeled “red.” The other part of the loop goes in the other direction, from the heart to the lungs, and is labeled “blue.” A second loop connects the heart to a "capillary bed" down below and has arrows to indicate that blood flows down one side of the loop and back up the other. The heart is divided into four chambers. Each loop starts in one chamber and ends in another.Example 7: Evaluating on internal coherence

The class had co-constructed a model of human circulation that involved 2 loops and a heart that had 4 chambers. One loop connected the lungs to two chambers. The other loop sent oxygen out to the body from a 3rd chamber and returned to a 4th chamber. But a student noticed that creating the 4 chambers had also created a problem: there was no longer a way for blood to flow in a complete circuit; it was now blocked by the walls added to create the chambers. (This led to a model modification.)


Run the model

The teacher can ask students to imagine the behavior of their model over time, to run it as a "mental movie." Students can then be supported to compare the results of that behavior with other known facts. This can be an especially powerful way to use mental imagery.

A humorous outline drawing of a human head and upper torso has been annotated by a student. A tube has been drawn leading down from the nose. The back of the mouth opens into this tube. The tube extends down into the chest and then divides into two tubes, one labeled "to lungs" and the other labeled "to stomach". There are other labels: “Nose,” “Saliva enzymes,” “Teeth Mouth Tongue,” and “Throat.”Example 8: Asking students to run the model

In a class where students were learning about the structure of the throat, one of the partial models constructed by the class had two tubes: one going to the stomach and another going to the lungs. The teacher asked the students, “Is the food going to the lungs?” By imagining how food would move in such a model (visualizing the behavior), students realized that their model needed something else to explain why food does not go into the lungs. Eventually, the class added a new element to their model. (This episode continues; see Example 1 under Support Modification.)


Thought Experiments

An especially sophisticated kind of prediction students can make from their models is a prediction about an unfamiliar system or unfamiliar behavior in a system. The goal is to see whether the model works in the new situation.

Example 9: A student runs a thought experiment

Some students had suggested that the rotation of the Earth either causes gravity or contributes to it. Although several students had disagreed, the proponents of the spinning model of gravity were not convinced. Then one student suggested the following.

A green ball has a curved arrow to indicate that it is spinning. A stick figure of a man has his feet taped to the side of the ball. He extends out sideways as though he is standing on the equator of a globe. He has his arms in the air (also out sideways) and appears quite happy to be spun around.S: Well, in reference to rotation and gravitational force, I think of them as being two opposite forces because if you stand on ... let’s just imagine a ball floating in space you tape your feet to. And you start spinning the ball around, you’re gonna feel like you’re gonna be thrown off. But if it’s a small ball, then the attraction between you and that little small mass is negligible so that you’re just gonna feel the forces being spun around in a centrifugal force.

This thought experiment is an imaginary case that allows one to separate the effects of spinning--which would be away from the ball--from the effects of the pull of a mass--which would not be noticeable here. This case supports the evaluation of the “gravity due to rotation” model, even though students have likely never experienced this particular scenario.

This kind of case often benefits from the use of I Visual Support Strategies, particularly strategies to support Mental Simulation.

Example 10: A teacher asks students to run a thought experiment

The teacher asked her class, “What is the main source of energy for the body?” She got back several answers: water, sunlight, food, exercise, sleep. She then proposed the following situation: A boat has been caught by a storm. One man survives and lands on a barren island. Although there is no food, the island has a lot of sunlight, shade to sleep under, a stream with clean water, and a long beach where he can run and exercise. The man weighs 200 pounds when he arrives.

The teacher then asked, “What will happen to him after a month on the island?” Students answered that he would lose weight, around 10 pounds. The teacher repeated the question but increased the amount of time. When the time became very long, the students predicted that the man would die. The teacher then asked the students, “Why does the man die if he has so many ways to get energy: water, sunlight, exercise, and sleep?!” The students replied that the man would die because there was no food. The teacher then asked, “So what is the only source of energy for the human body?” and the students answered, “Food.”    

Example 11: Another teacher request for a thought experiment

Example 6 above is also a request for a thought experiment.


Supporting and Contributing Strategies

Most of the processes above involve mental animation. There are a number of visualization strategies teachers can use to help students Run the Model or Use Thought Experiments. See:

I. Depictive Gestures
I. Scientific Drawings
I. Mental Simulations

Different Participation Strategies may be needed at this point in the lesson.

I. Participation Strategies


Articles, Papers and Websites

More in-depth discussion and more student examples are found in the following papers by our team:

Generating, evaluating, and modifying scientific models using projected computer simulations (Price & Clement, 2014)

Documenting the use of expert scientific reasoning processes by high school physics students (Stephens & Clement, 2010)