One of the largest investigations of elementary education ever undertaken, the Sustaining Effects Study sought answers to a series of policy questions. The two major issues addressed by the study were (1) Who receives compensatory education (CE)? and (2) How effective is CE? Related to these primary issues were a number of secondary questions: (3) What is CE? (4) What is the nature of the process of classroom instruction in elementary education? (5) What happens to the achievement of students when their CE services are discontinued? (6) Is there an optimal duration and period for receipt of CE services? (7) What happens to student achievement over the summer, and is summer school effective? (8) What is the nature of the home environment of elementary school students? and (9) What are the relative contributions of socioeconomic background and schooling toward school achievement? To obtain answers to these questions, a large amount of data was gathered through a complex design. Five substudies were initially planned: a longitudinal study assessing educational achievement for 3 consecutive years; a study of successful instructional practices in high-poverty schools; a study of participant characteristics and relationships among economic status, educational need, and instructional services received; a cost-effectiveness study focusing on resources and services to which students were exposed during reading and math instruction; and a study of the effectiveness of summer school programs. A sixth substudy was added later and involved following a limited sample of students into their high school years. Numerous instruments were used to gather data from students and teachers. (Specific study designs, variables investigated, and results obtained are discussed.) (RH)