Discussed in connection with Project PRIME (Programmed Reentry into Mainstream Education) is the need for educational research to assess the comparative efficacy of three instructional settings (regular resource, and self-contained special education classes) for providing services to handicapped children. It is explained that data on the classroom ecological structure (including physical environment, personnel, group structure, and instructional activities) were gathered from observations of teachers in approximately 400 regular, 100 resource, and 150 self-contained classrooms. Noted among findings were differences between regular and special classes in the number of students and instructional personnel (which affected grouping patterns and instructional approaches), and stressed was the need in future analyses to study the effect on student outcomes of each ecological characteristic, both singly and in interaction. (LH)