Scientific method is about developing and evaluating explanations through experimental evidence and modelling, says the national curriculum. But even the most experienced science teachers find the process of designing, building and evaluating a model for a scientific concept both challenging and thought-provoking. We believe the key is to think in terms of "a good enough model". Although any model has its flaws, it is still a useful teaching style if you encourage learners to analyse and evaluate their models and suggest ways they could improve them.
The following is a favourite example of ours, developed to encourage Year 8 pupils to link the ideas from QCA units 8A (food and digestion) and 8B (respiration).
Resources:10-20 balloons, inflated and tied into groups of three or four; sticky labels with the word "oxygen".
Model gut: three or four pupils sit around a table where they "receive" the "food" (groups of balloons) from a pupil who is the "mouth". The "gut" pupils then "break up" the "food" into molecules (balloons) of glucose.
Model circulation system: seven or eight pupils walk around the room in a set pathway visiting the "lungs" and collecting "oxygen" labels. As they then pass the "gut" they collect molecules of glucose (balloons) and stick the oxygen labels on them.
Body cells: a selected group of boisterous pupils with the job of being "body cells" sit around the edge of the room. The "blood" carries the glucose balloons with oxygen labels on them to give to the body cells, who then release the energy by popping the balloons.
Waste products of respiration: As the "blood" circulates it collects the popped balloons, which now represent the "carbon dioxide", and comment that they are "wet" - this being the other waste product, "water". The "blood" then carries the "waste products" and places them into the "lungs".
This has limitations, as do all models, but discussion can follow, with pupils talking about why it is a "good" or "bad" model and think of alternative ways to do it. It provides a mechanism to link ideas about respiration with ideas about circulation and the part played by the lungs and the digestive system. It often leads to in-depth discussions about the interrelationship between body systems.
Andrea Dart Head of science at Broad Oak High School, Bury, Lancashire
Libby Mooney Science teaching and learning consultant, Bolton