Data were drawn from a 3-year longitudinal study of students who were attending 6 California high schools from 1987 to 1990 (n=3,761). The schools selected represented a diverse sample in terms of size, location, socioeconomic background, and ethnic composition. Researchers returned to the same school for 3 consecutive years, which allowed the tracking of individual students over time. All students in the six schools were invited to complete a self-report questionnaire that focused on school-related behavior and measures of family relationships and parenting behaviors, peer relationships, deviance, and psychological adjustment. Approximately 4 percent of the students in attendance on days the questionnaire was administered chose not to participate. Participation in school-based extracurricular activities was based on students' reports of such participation during the current school year. Time spent in such activities was also determined. Life-events stress was measured through student reports on the number of stressful life events experienced during the past 12 months. Other variables measured were substance use (tobacco use, marijuana use, alcohol use, or a drug other than marijuana), depressive symptoms, and academic performance and orientation. Cross-sectional findings indicate that participation in extracurricular activities was associated with more positive outcomes for all variables but alcohol use and depression, controlling for gender, ethnicity, and grade in school. Within-person analyses found year-to-year covariation of extracurricular participation and positive outcomes. 5 tables and 46 references