Materials natural and processed (vignette)

​The following vignette is reproduced with permission from of Peel Publications, Australia, copyright © 2007.

Why don't we make underwear out of glass?

Students construct and enter science (and other) classrooms with explanations for the world around them that are very sensible from their point of view and from the experiences that they have had. I spent the last 17 years of my school science teaching career developing and refining (and borrowing) techniques for bringing these ideas out and using them in the classroom.

Perhaps unfortunately, most of these ideas are in conflict with accepted science (only ‘perhaps’ as many of my students ended up believing that they learnt more and better when they ended up changing their views). As a result, there are a whole raft of procedures that focus on clarifying ideas, retrieving and then generating 'cognitive dissonance' - encouraging restructuring of these ideas: PEEL strategies B1 Predict Observe Explain, B8 Probe of prior views, B13 Challenge of ideas, B3 Interpretive Discussion, B17 Return to Prior Views and B6 Return to the Discussion all have this focus on changing students' ideas.

There are a few areas however, where the explanations that students construct are consistent with accepted science. One of these is in the area of materials and their properties - a 'big idea' that matters to me is that all materials have properties and these properties determine their uses. All students have many specific examples of this idea, but my problem was that these experiences were very tacit and were not organised in the way just described.

To elicit these ideas I decided to 'make the familiar strange' - to re-present phenomena that were familiar in a way that highlighted these tacit ideas. I used a series of questions about materials and their use designed to allow us, as a class, to explicate and codify what they knew - which was most of what I wanted to teach.

The question, "Why don't we make underwear out of glass?" got us off to a great start.

"Oh Yuk! That would be stupid!"

"Why?" I pushed.

"Glass underwear would break."

After a short discussion the word ‘brittle’hit the board.

"It would cut us." A bit more discussion about what property this implied led to ‘hard’.

"It won't bend." – ‘Rigid’.

We built up a dozen properties of glass that were unsuited to underwear. I had a series of similar questions designed to bring out what I regarded as a reasonably comprehensive list of properties of materials relevant to their uses;

  • Why don't we make nails out of rubber?
  • Saucepans out of stone? and so on.

The board was soon full of words and phrases describing properties. The next task was to sort these into pairs of opposites:

  • hard/soft
  • good heat conductor/poor heat conductor
  • rigid/flexible
  • easy to shape/hard to shape

Many pairs were already on the board, but many weren't - only one term was and a need was generated for the 'opposite' - e.g. What is the opposite of brittle?

The end result was that the students recognised that they did not need to learn my big idea about materials, properties and uses as 'new' knowledge, rather they just needed to reorganise their own experiences against this construct.