Studies done in the 1960s and 1970s which sought to compare middle schools with junior high schools were ineffective. Intended to fill the frequently noted research void in the middle school movement, this monograph summarizes previous research on the effectiveness of middle level schools and presents results of a 1993 study on middle schools conducted by the authors. Part 1 of the monograph provides an overview of early research in middle level education and describes the outlier research approach. The results of several studies conducted up to 1994 are detailed, providing substantial evidence to support the efficacy of the middle school concept. Part 2 describes a 1985 study of 130 middle schools which had been deemed especially successful. The major findings are outlined: Middle level schools judged by others as outstanding display team organization, teacher-based guidance activities, flexible time use, faculty participation in decision-making, and other tenets of the middle school concept, and positive results are evident in academic achievement, school climate, faculty morale, and student behavior. Part 3 describes the 1993 study conducted by the authors. Comprehensive reports from 108 schools are analyzed to reveal the presence of and the effectiveness of middle school components that are widely recommended for schools serving 10-15 year olds. Part 4 completes the monograph with a summary statement and conclusion, noting that practitioners can continue to expect implementation of middle schools to result in improved academic achievement, positive personal development, and enhanced citizenship for its students, but that such goals will not be easy to achieve. (Contains 54 references.) (KDFB)