The purpose of the project was to develop a schema-based model of teaching and learning and to test the adequacy of that model in a computer-based instructional system. The domain of instruction is arithmetic word problems, and the schemas center on the situations that can be expressed in such problems. A core set of situations was identified, and a series of studies verified that the situations were sufficient for describing virtually all legitimate work problems. A model of schema knowledge was constructed for each of the basic situations. Each schema model specified the feature knowledge, constraint knowledge, planning knowledge, and implementation knowledge required to use the schema successfully.