III Modeling Phases: Modify Model

The goal of this modeling phase is to have the class modify the model to help it provide a better explanation for the phenomenon.

What characterizes this modeling phase is that the focus of classroom activity is on modifying aspects of the model that students have evaluated as needing improvement. There are a number of Level II Creative Reasoning Processes that can help with this modeling phase.

This phase can rapidly alternate with the Evaluating a Model phase and these two phases can work together to support Level IV classroom modes. However, at times a teacher may want the class to focus on modifying. In the first example below, the teacher directly challenged the class to come up with a modification to solve a question she had about the model. In the second example, the class had gone through an extensive evaluation phase where they had decided that many aspects of the models currently on the board were problematic. At a certain point, the teacher decided to call a halt to the evaluation of those flawed elements and did so by erasing them. He then challenged the students to come up with some different ideas

Example 1

When modeling the lungs, after considerable discussion and help from their teacher, 8th graders had evolved a model with tubes that took air to many cavities (alveoli). In the cavities, air was near to blood vessels (capillaries). The teacher then challenged them, “But how does oxygen get into the blood vessels from the cavities?” This was a direct request for model modification.





Two ideas proposed for modification were “little pipes” from the alveoli to the capillaries (pictured) and “oxygen...seeping through the walls.” These were each evaluated, returning to the Model Evaluation Phase in cyclical fashion.

Hand-drawn lungs are filled with squiggles, showing that they are not hollow. There are also small grape-like clusters of alveoli at the ends of branching tubes. However, there is no indication how anything could get from these internal structures to other parts of the body. No blood vessels have been included in the drawing.
a. Model of lungs with tubes to many alveoli. "But how does oxygen get into the blood vessels?"

A capillary is shown surrounding an enlargement of 4 alveoli.  The alveoli look like grapes with small tubes leading to the capillary. Circles inside the capillary represent blood cells. Tiny pairs of circles represent O2 and are inside each alveolus, inside the capillary, and inside the blood cells within the capillary.
b. One idea: Model of alveoli with "little pipes" to a capillary.

Example 2

(Fig. a) Students had evaluated two possible models for the human circulatory system. (See Model Competition Example 1). As a result of their evaluation, they had decided that neither model worked. The teacher suggested erasing all the connections that differed between the two models. For the Model Modification phase, the class began to suggest new ideas for how the lungs might be connected to the heart and how the blood might return from the cells of the body to pick up more oxygen.




(Fig. b) After an extensive Model Modification phase, the resulting model had a two loop system.




(Fig. c) One final modification occurred when a student spontaneously walked to the front of the room and erased holes between the upper and lower chambers of the heart, providing a complete, complex pathway for the blood through the entire system.


Although this part of the discussion was focused on modification, there was actually a frequent back and forth between modification and evaluation, as each new model element was evaluated before the class agreed to add it. These included three blood vessels, the color codes for each (to determine oxygen rich or poor), designations as arteries or veins (determined by whether they travel away from or to the heart, not whether they are oxygen rich or poor), vessels inside the lungs, and finally the valves inside the heart.

This discussion used several Level II strategies to support Model Modification, in particular, Adding or Subtracting Model Elements.

A simple chalk outline of lungs is in one part of the picture. In another part of the picture is a simple outline of a heart with 4 chambers, a "capillary bed" consisting of three short lines, and a line, representing a blood vessel, connecting the heart and capillary bed. Anything connecting the lungs with the rest of the image has been erased, leaving a blank space in the middle of the picture.
a. Model at beginning of modification phase.

The drawing is as above (Fig. a), with the addition of blood vessels. These vessels form two loops, one connecting the lungs and heart and the other connecting the heart and capillary bed. Vessels are shown going in and out of both lobes of the lungs, and either in or out of each chamber in the heart. Arrows show the direction of blood flow and the pulmonary vein and artery between lungs and heart have been labelled to show that in this case, the vein would be Red, with oxygen-rich blood, and the artery would be blue, taking spent blood to the lungs to get more O2.
b. Model after many modifications.

A little opening has been created between the left auricle and ventricle and between the right auricle and ventricle. These openings were spontaneously created by a student in order to show how the blood flows through each side of the heart in a two-loop pattern.
c. Model after the final modification. Note the holes between the upper and lower chambers of the heart; the route the blood takes through the chambers can now be seen clearly.


Supporting and Contributing Strategies

Reasoning processes and strategies that support this phase of the modeling sequence are found in:

II Creative Reasoning Processes to Support Model Modification

Suggestions for managing a type of discussion that can be very useful here are included under:

I. Participation Strategies

There are many Visualization strategies that may be helpful. Among them:

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



A discussion of this modeling phase in the context of a classroom example is in Core of this Approach.

For how this phase fits into the larger framework, see the Level III section of the Educator's Tour.

For more discussion on the theoretical underpinnings of the framework, see the Introduction to the Full Theory page.


Articles, Papers and Websites

More in-depth discussion of this modeling phase is found in the following paper by our team:

Large scale scientific modeling practices (Nunez-Oviedo & Clement, 2019)