Both the junior high school and the middle school were established specifically to meet the unique physical and intellectual needs of preadolescents and early adolescents. The ability of these types of schools to accomplish that goal, as measured by the research, is the basic subject of this report. Each of the report's five parts begins with an overview of the contents of the section and concludes with a summary of the major research studies discussed in the section. The first part considers theories related to grade organization, portrays the variety of organizations tried, and ponders the implications of population projections for grade organization flexibility. Part 2 treats the appropriateness of different grade organizations given the physical, emotional, and mental development of children entering adolescence. The third and fourth parts trace the evolution of the junior high school and the middle school, respectively, into their present forms. The final part details the research comparing junior high and middle schools in terms of their effects on students, teachers, administrators, and educational quality. (PGD)