This final report summarizes work done to formulate and test some cognitively-based principles useful for designing instruction in scientific or engineering fields. These principles stress the coherence and interpretability of the knowledge acquired by students. The principles were specifically applied to: (1) analyze the underlying knowledge and thought processes needed to interpret scientific concepts effectively; (2) investigate how actual experts and novice students interpret such concepts; and (3) devise and test instruction designed to teach such concepts more effectively. Attempts were also made to devise computational environments to explore and implement these instructional ideas. (Author/RH)