Noting factors that have contributed to an increased emphasis on developmentally responsive middle level schools, this revised monograph examines early adolescence as a developmental period and explores the physical, psychosocial, and cognitive characteristics of 10- to 15-year-olds. In addition, the monograph provides recommendations concerning how middle level schools can provide developmentally appropriate educational experiences. Chapter 1 explores early adolescence as a developmental period, and its evolution toward acceptance. Contemporary efforts to promote the 10- to 15-year-old period are described. Chapter 2 examines contemporary research on physical, psychosocial, and cognitive development, and provides a developmental portrait of young adolescent learners. Chapter 3 shows how young adolescents' physical, psychosocial, and cognitive developmental characteristics can form the basis for developmentally appropriate curricular, instructional, and organizational decisions in middle level schools. Chapter 4 highlights resources for middle level school educators, including professional associations, Internet sites, and resource centers. Appended is a checklist for determining middle level schools' response to young adolescents' developmental characteristics. (Contains 110 references.) (HTH)