The idea of organizing secondary schools into smaller units has gained support in the last decade. This guidebook is designed to support efforts to develop an effective small-unit plan for high schools. The first two sections highlight the benefits of small-unit organizations and identify the institutional barriers to implementation. Proponents of small-unit organization argue that it dispels alienation, supports a more coordinated and concentrated instructional approach, and offers teachers more input into the decision-making process. Challenges center around administration, assignment of students to core-curriculum teachers, student support, and teacher roles. The third section details the essential features of small-unit organization--instruction, student support, physical facilities, and unit management. The fourth and fifth sections provide examples of two schools that have successfully implemented small-unit plans--the Koln-Holweide Comprehensive School in Germany and William Penn High School in Philadelphia, Pennsylvania. Five tables and two figures are included. The appendix contains additional planning resources. (LMI)