The Instructional Design Environment (IDE), a computer assisted instruction tool for instructional design, has been incorporated into the curriculum and instructional development in mathematics instruction in the Stanford Teacher Education Program (STEP). (STEP is a 12-month program leading to an M.A. in education which emphasizes content focus and reflective and collaborative teaching.) Previously used as an industrial instructional analysis and development tool, IDE has now been used as a tool for teacher training. It uses hypermedia-style representations of subject matter and an instructional design model that students use to develop curriculum and organize courses. The results of using IDE include: (1) students are prompted to follow the instructor's design guidelines and standards; (2) continual feedback between students and instructor can be provided; (3) participative decision making between students is promoted; (4) reflection among students as to the effects of their decision is promoted; and (5) exploration of subject matter arrangements is possible. Students using IDE for curriculum development in mathematics are willing to explore alternative lesson organizations, have a deeper understanding of the subject matter, and think more about instructional design practice. An example of an instructional model, a lesson card, a rationale card, and a subtopic card are appended. (4 references) (DB)