The University of Alabama

Teaching Science

Dennis Sunal

 

Using Metaphors, Models and Analogies in Teaching Science: A Review of the Literature


            Observation of science teaching in many classrooms, suggests that use of models and analogies may produce as much good as harm, creating acceptable student understanding at the same time generating misconceptions and causing more confused learning. Research has identified the problems for student understanding caused by the inappropriate use of analogies.  Research suggests that the use of a teaching strategy for the presentation of models, metaphors and analogies will enhance student understanding and reduce misconceptions.  One of these is Glynnís (1991) model of Teaching-With-Analogies (TWA), a model developed from an analysis of science textbooks.

 

The Teaching Strategy

 

            The idea familiar to the students will be labeled the analog model. The science idea to be learned will be called the concept.  Links between the analog model and concept, with shared and unshared attributes, are called mappings.
            While each step is important, the order in which the steps are used depends upon the teacher's style, the particular scientific concept, and the analogy being used.   In its general form, the systematic approach for teaching with analogies is as follows:


            Step 1--Introduce the concept to be learned (ie. through the exploration and the beginning of the invention phase of the learning cycle).  Give a brief or full explanation depending on how the analogy is to be employed.
            Step 2--Review with the students' the analogous situation.  Introduce the analog model so that its familiarity to the students can be estimated by discussion and questioning.
            Step 3--Identify the relevant features of the analog model.  Explain the analog model and identify its relevant features at a depth appropriate to the students' familiarity with the analog model.
            Step 4--Map out the similarities between the analog model and the concept.  Teacher and students both must identify the relevant features of the concept and link these with the corresponding features of the analog model.
            Step 5--Indicate where the analogy breaks down.  Note alternative conceptions that the students may be developing and known areas where the analog model and concept do not correspond.  Point these out to the students to discourage incorrect conclusions about the concept from the analog model.
            Step 6--Draw conclusions about the concept.  Summarize the important aspects of the concept.           

            At Step 1, three approaches are possible.  When the analogy is used as an advance  organizer, the concept is introduced after the analogy.  When the analogy is used to develop the concept, the concept should be taught in sufficient detail to make the analogy relevant.  When the analogy is used as a revision, the concept is fully taught.  Teachers can enhance analogical instruction by choosing an appropriate analogy before the lesson and carefully planning how it will be taught and used.  Steps 2, 4, and 5 are the points where student understanding often fails to match the teacher's expectations.

 

Teaching with Analogies


            It is generally recognized that analogies generate meaning through a constructivist pathway (Duit, 1991).  Although students come to science with tenaciously held intuitive ideas and beliefs about science-related phenomena before they have experienced the relevant formal teaching, the students' ideas are often ignored by teachers; consequently, students derive meaning from an analogy that is often incompatible with the teacher's view.  It is imperative that teacher and student hold a common view of the analog model before mapping begins.  Thus, at Step 2, if the student visualizes the analog model in a different way that the teacher, it is no wonder that the student generates alternative conceptions.  Teachers draw on a far richer knowledge base than do their students, and there may be distinct cultural and socioeconomic differences as well that can lead to misconceptions.
            As a teacher becomes proficient in the use of this teaching sequence, he or she may unite Steps 3 and 4 as a single step.  As relevant features of the analogy are identified (Step 3), they are often mapped immediately as the first of the shared attributes  (Step 4).  Our in-class observations show that student mapping of the shared attributes cannot be taken for granted.  Additional shared attributes that were not immediately apparent became so as the analogy was discussed in class, and, on several occasions, weaker students made valuable contributions to the mappings that had been overlooked by more able students.
            Post-lesson student interviews can be of value for examining unshared attributes.  Every analogy breaks down somewhere, and many analogies employed in science are used for phenomena that are foreign to students.  It is unreasonable to expect novices to make expert judgments on structures or functions that they cannot see or even visualize.

            Students reported that they were much more comfortable with their understanding after the teacher had identified the unshared attributes of the analogy.  It is also expected that teachers may perform Steps 4 and 5 as a parallel exercise because, as students propose analog model-concept mappings, shared and unshared attributes will emerge side-by-side.
            Step 6 is necessary because it articulates what has been found by carefully relating the familiar to the unfamiliar.

 

An Example


Homeostasis is like a student walking up a descending escalator.
The following account describes how a teacher might present this analogy using our systematic approach:
            (Step 1) -- Homeostasis is the process by which living things balance input and output to maintain a constant internal environment.  When input and output are balanced, the internal environment is in dynamic equilibrium.  In this way, organisms actively maintain such things as temperature, water, O, CO, and blood glucose levels.  As all living things are active, these items only remain constant because the amount taken in (being produced) equals the amount being consumed (removed).
            Let's study the maintenance of body temperature.   Our body processes work best when our internal temperature is 37 degrees C.  If our body temperature varies by more than about 3 degrees C in either  direction, we  can die.
            (Step 2) -- Are you all familiar with escalators, the moving stairs that are found in many department stores?  Imagine a student walking up an escalator that is moving down.  What will happen?
            (Step 3) -- If the student walks up the escalator at the same speed that the escalator moves down, she appears to an external observer to stand still.  The student and the escalator are in equilibrium/  If she walks up faster than the escalator goes down, she slowly moves up, but if she walks slower than the escalator, she moves down.
            In both cases, there is no equilibrium.  Equilibrium can only be restored by altering the student's velocity so that it is the exact opposite of the escalator.
            (Step 4) -- Normally, we lose heat by conduction to the air from our skin and lungs, which is like the escalator constantly moving downwards.  Internal heat is continuously produced by cellular respiration, like the student walking upwards at a normal walking speed.  When the rate of metabolic heat production equals the rate of heat loss to the air, temperature remains constant just as, to an external observer, the student appears to remain at one level even though she is walking up as the escalator moves down.  (This is a state of equilibrium).
            If we stand in sunlight or close to a heater, we gain extra heat, and this is analogous to the student walking faster.  If our rate of heat loss to the air remained constant and nothing else changes, our temperature would rise, and, just as the student ends up at the top of the escalator, we would overheat and die.  Normally, we would not overheat in this way because we begin to perspire, and as the sweat evaporates, we cool down.  This is analogous to the student slowing down to maintain a constant level on the escalator.  When we get too hot, we slow down to rest and restore equilibrium.
            If we were left unprotected in an icy wind or cold water, we would lose heat much faster, as if the escalator moves down faster than the student walks up.  Soon she will be a the bottom (death from hypothermia).  If the cooling is not too severe, we can increase our muscular activity to produce extra heat and balance the loss, which would be like the student running up the escalator, since increased production balances greater loss.
            (Step 5) -- The way this analogy was used, the top and bottom of the escalator represent high and low temperatures respectively.  The analogy suggests that, provided the student walks up as fast as the escalator moves down, acceptable equilibrium is possible at any temperature (any level of the escalator).  This is not so, however, because every homeothermic animal has an optimum temperature.  Another factor that has been ignored is that, as body temperature rises, heat is lost faster to the air because there is a greater temperature difference.  As body temperature falls, the rate of heat loss falls.
            (Step 6) -- Equilibrium in living things is an active process involving balanced input and output, with the rates of input and output being equal but in opposite directions.


Summary


            Presenting analogies with a planned teaching strategy has the potential to enhance student understanding of science concepts while reducing the incidence of misconceptions being formed.  Effective teaching using analogies appears to contain at least three active steps: (1) ensuring that the teacher and students visualize the analog model congruently, (2) developing the shared attributes to plausibly elucidate the concept, and (3) clearly identifying unshared attributes for the students.

 

References

Duit, R. (1991), On the role of analogies and metaphors in learning science, Science Education, (75), 649-672.

Glynn, S. (1991), Explaining science concepts: A teaching with analogies model.  In S. Glynn, R. Yeany & B. Britton (Eds.) The psychology of learning science. pp. 219-240.

Harrison, A.G. & Treagust, D. F. (1993), Teaching with analogies: a case study in grade 10 optics. Journal of Research in Science Teaching , 30(10), 1291-1307.

Harrison, A.G. & Treagust, D. F. (1994), Science Analogies. The Science Teacher , April, 40-43.