In many of our lesson units, students are presented with two competing scientific models and a body of evidence. As in many cases in the real world (“Which diet works best?” “what is the best model to explain global temperature data?”), students must use evidence to choose one model or models that best fit with most of the relevant evidence.
We have found that competing models help students to think systematically about how different models are related to the same body of evidence. They learn that some evidence can support two more more models, whereas other evidence may support one model and contradict the other, and still other evidence may support one model and be irrelvant to the other. Students learn that rival models can sometimes interpret the same evidence in different ways.
Competing models work well on topics where students lack extensive prior knowledge and thus cannot readily develop their own models prior to instruction. Competing models also work well when we want to deliberately highlight a key feature of the normative model, by contrasting a model that has that feature with a model that lacks that feature. For example, we have contrasted models of natural selection that include the selective pressure with models that lack the selective pressure. In this way, students realize that the model lacking any selective pressure fails to explain some critical evidence about selective pressures and so is an unsatisfactory model.