A user-based research and programing process was undertaken to identify environments supportive of mainstreaming handicapped students. This report first describes the range of strategies that have been developed to implement mainstreaming programs in public schools, then develops a guide for designers to help them understand the educational and developmental needs of handicapped children. Types of handicaps, their incidence, and their nature are explained. The identified critical design principles for mainstreamed schools were derived from a review of the scientific and professional literature and behavioral observations and interviews. The report then presents a set of 18 design principles for the programing and design of environments for mainstreaming, each with supporting research-based arguments and detailed criteria. Drawings accompany the design criteria and a bibliography concludes the report. (Author/MLF)