This report describes approaches used by schools to prevent or reduce gang involvement among schools. The study of gang prevention and intervention builds on a large-scale National Study of Delinquency Prevention in Schools. A sample of 1,279 schools participated in the study. Overall, 7.6% of the male and 3.8% of the female secondary students reported that they had belonged to a gang. A description is provided of students' involvement with gangs, the characteristics of students who are involved with gangs, and the extent and correlates of gang problems in schools. An explanation is also given of what and how much is being done in schools to prevent or reduce gang-related problems, and to assess how well these prevention and intervention activities are being performed. It identifies features of prevention and intervention activities that local schools and communities can consider to strengthen their programs. Tables are used throughout to explain the types of gang prevention activities available in schools. (Contains 2 appendixes, 36 tables, and 149 references.) (JDM)