Building Functional Models: Designing an Elbow.
Penner, David; Giles, Nancy; Lehrer, Richard; and Schauble, Leona.
Journal of Research in Science Teaching. Vol. 34. No. 2. PP 125-143. (1997)
The idea of modeling or model building is a topic at least touched
upon in nearly all science classrooms. The effectiveness of model
building as a learning device depends on how effectively student
embrace the true meaning of "modeling."
Most students believe that "science" consists of observing
and recording-scientists make observations and accurately record
those observations. According to student perceptions, keeping
complete records is the key to scientific discovery. Students
also believe that observing is "non-participatory"-models
to them are copies of physical phenomenon.
However, most working scientists are model builders-their lives
tend to be dominated by building and testing models. Scientists
know that models channel observations and drive interpretations.
For the purpose of this paper, models can be defined in two ways:
- The model looks like the "real thing."
- The model performs the correct function of the "real thing."
Penner, Giles, Lehrer, and Schauble chose the problem of how the
human elbow works to be investigated via model building. Before
beginning model building, students did guided research. The students
determined that not all mammalian "elbows" are the same
in either form or function. This was a key finding, since it invited
a more open-ended approach to student model building.
Key points to emphasize when teaching through model building are:
- Models are not merely representations of something.
- Evaluation and change are important in model building, and not just for the fixing of mistakes.
- Model-based reasoning takes time to develop.
For this study, a variety of materials were made available to
students for use in model building. Cardboard tubes, Popsicle
sticks, modeling clay, Styrofoam balls, hinges, springs, wooden
dowels, flexible strips, tongue depressors, balloons, rubber strips,
door hinges, posterboard, and glue were among the materials made
available. Some items were deliberately included because of their
match with structural features (e.g., dowels could represent arm
bones). Others were included because they matched with perceptual
features (e.g., Styrofoam balls matched the "bump" at
the base of the elbow).
Students were given three 1-hour sessions on consecutive days
to complete "more than one solution" to their model
building problem. After building initial models in groups, results
of these group projects were presented to the class. Time was
given to revise or modify designs as groups desired.
Two groups of students were interviewed after the model building
sessions: 1) model builders and 2) non model builders. During
the individual student interview, each student was shown four
"sample" models: two tongue depressors in a clay ball,
a flexible drinking straw, a drawing of the elbow, and two pieces
of posterboard hinged together with a string running through them.
Ratings were given to each model in answer to a question on the
functionality of the model (1 being "did not like" to
5 being "liked a lot").
There was some similarity between groups in rating the sample
models. For example both groups liked the cardboard/string model
best. There were differences between groups as well-model builders
were much less pleased with the picture than were non model builders
of similar age.
The most significant finding regarding the model-rating was in
the types of critique-comments provided by students. There were
statistically significant differences between the two groups-model
builders were more likely to provide justification with a constraint
than non model builders. In other words, model builders were better
able to explain what the limitation of a model was than were non
As an example of this type response, consider the flexible drinking
straw model. Based on their model building experiences and subsequent
revision of models based on class discussion, model builders disliked
this model because it did not limit backward-bending motion "like
a real elbow." In addition, non modelers of the same age
as the model builders universally failed to see why lack of functionality
(in this case backward bending of the joint) was a major flaw
in a model.
The study focuses on children's attempts to understand the function
of their elbows through a process of model-based design. Via discussion,
model building evaluation, and revision, children came to understand
that not only motion, but also constraints on motion were important
qualities to include in their models. [
] In comparison to
a nonmodeling peer group, modelers were largely able to ignore
perceptual qualities when asked to judge the functional qualities
of models. Further, they showed an understanding of the modeling
process in general that was similar to that of children 3-4 years
older. - p. 141
Oh, did I mention that the students in the study were first and
I suspect you are wondering how a study on early elementary students
has any application to middle and high school students. Here's
how: "In fact, the ideas held by middle and some high school
students [reported in previous studies] seem to be the same
as those held by our nonmodeling second graders [emphasis
mine]. They shared a propensity to evaluate models by assessing
their perceptual similarity to the phenomenon of interests."
- p. 141
So what's the bottom line here?
I would hope that we want our students to function beyond the
second grade level in as many areas as possible by the time they
finish our classes. If model building and testing are central
constructs to the process of science, we need to expose our students
to those methods. However, simply saying "build a model"
is not enough. There needs to be a sequence of "discussion,
model building, evaluation, and revision" where students
are allowed to explore multiple models that reflect both structural
and functional qualities of whatever is being modeled.
I encourage you to consider where in your curriculum you provide
time for students to proceed through a pathway like the one described
above. If you find such pathways missing, where could one be included?
When you include model building in your curriculum, don't let
your students off the hook when it comes to critiquing models
designed by themselves or classmates-be sure to ask about the
constraints of the model presented. You can use as an example
of such critiquing that, while a flexible drinking straw is a
model of the human elbow, it is limited in effectiveness because
it allows for flexion in any direction, and the human elbow allows
flexion in only one direction.