The middle school concept was devised to counteract the tendency of junior high school programs to mimic those of the high school at the expense of addressing the developmental needs of students who are in the process of physical maturation. This book on curriculum design focuses on the importance of the middle school and understanding preadolescent students at this intermediate level of education. It considers an effective middle school as one which breaks down the barriers of departmentalization and concentrates on learning and teaching across the disciplines. To enable such an environment, the booklet suggests that educators consider the developmental needs of the preadolescent, and outlines a basis for curriculum design to meet these needs. The booklet examines developmental characteristics in the following areas: Cognitive Skill--Brain Development; Cognitive Skill--Language Development; Affective Development; Social Development; Aesthetic Development; and Physical Development: Growth, Health, Body Management. Each characteristic is presented in terms of: (1) opportunities needed for healthy development in each area; (2) characteristics of emerging adolescents related to each area; (3) implications for the education of preadolescents; and (4) curriculum implications. (BAC)