When students have rich prior ideas of their own about a topic, we often have the students create their own initial models, before they have seen much or any evidence. For example, in our genetics unit, an early activity is that students individually develop their own models to explain how traits are inherited.
Each class of students will tend to produce a set of models that falls into several types. For example, in the genetics unit, most student models fall into common categories (examples to the right and below).
Teachers can then choose two or three of these models, and then students can use evidence to choose among the models. They may also find that they need to revise the best model, because even the best model cannot explain all the evidence without some revisions.