Models are created and evaluated based on evidence sets. The evidence is either collected by students or provided in the materials. Evidence varies in quality from well-conducted experiments to anecdotal accounts.
PRACCIS materials engage students in multiple opportunities to practice and improve their argument writing skills; using evidence to support or refute a model (claim) and providing good reasons.
PRACCIS materials include a suite of scaffolds aimed at helping students create good models, evaluate models and evidence, and relate evidence to models.