The study found that participation in organized activities during early adolescence was associated with higher than expected grades, perception of the importance of school for the future, self-esteem, resilience, and association with prosocial peers, as well as lower than expected risky behavior. There were variations within this general finding, depending on the nature of the activities in which the youth participated. Participation in middle-school clubs was positively related to academic adjustment at 8th and 11th grades. Participation in 8th-grade school sport was associated with lower school value than among non-athletes in the 8th and 11th grades. Participants in 8th-grade school sports had more problem behaviors than did nonparticipants. Participation in 8th-grade school clubs was a positive predictor of resiliency and prosocial peers at both 8th and 11th grades. Involvement in eighth-grade school sports predicted an increase in resiliency over time; and involvement in 8th-grade out-of-school recreation activities predicted a lower than expected decline in self-esteem 3 years later. There were more similarities than differences in the relationship between participation in organized activities in 8th grade and developmental outcomes at 8th and 11th grade by race, gender, and socioeconomic status. The findings of this study, along with those of prior research, support the encouragement of involvement in organized activity in the middle-school years across a diverse group of youth. The sample included 1,047 youth (51 percent female, 67 percent African-American, and 33 percent European-American). Analysis of covariance techniques examined links between participation in 8th-grade school clubs, school sports teams, and out-of-school recreational activities and adjustment at 8th and 11th grades. 4 tables, 3 figures, and 59 references