This paper traces the historical development of the middle school from its beginnings in 1893. It presents philosophical background for the middle school concept and compares middle schools and junior high schools. Psychological theories underlying the middle school are discussed, including the theory of the period of "transescence" between childhood and adolescence. Practical considerations involved in instituting a middle school are listed, beginning with initial decisions about objective-setting, grade span, public relations, staff selection, curriculum, facilities, and long-range planning. The need for special teacher training is stressed. Guiding principles for a middle school regarding grading, student involvement in decision-making, learning objectives, encouragement of creativity and diversity, and interdisciplinary experiences are offered. A need is recognized for functional models for middle school programs, organizations to aid planners, and research yielding insights into local needs for a middle school program. (JM)