This book examines the qualities of schools that successfully deal with the developmental diversity of young adolescents (10 to 14 years old). In part I, the author reviews literature on school effectiveness and develops a framework for evaluating schools that are not simply "effective," but are "successful." Seven criteria are outlined: (1) better than average standardized test scores; (2) low absentee rates, (3) low incidence of vandalism and victimization; (4) few or no destructive graffiti; (5) low suspension rates; (6) parental satisfaction; and (7) a reputation for excellence. Part II presents case studies of four middle schools which meet these criteria and were studied by the author. The schools are Western Middle School (Almanace County, NC), Dorothy L. Fisher Magnet Middle School (Detroit, MI), Samuel V. Noe Middle School (Louisville, KY), and the Shoreham-Wading River Middle School (Shoreham, NY). Part III summarizes recurrent themes in these successful schools. Areas discussed include purposes, goals and definitions; the principals; school climate; curriculum and instruction; school organization; and the schools' positions in their communities. The most striking feature of the successful schools studied is said to be their willingness and ability to adapt to individual differences in their students' intellectual, biological, and social maturation. (GC)