The evaluation found that participation in substance-use prevention activities in nonschool hours (after-school programs, summer camps, and prevention-related extracurricular clubs) was related to a decreased likelihood of tobacco, alcohol, marijuana, and inhalant use among Indiana youth. Among middle-school students, the prevention activities were related to a lower likelihood of tobacco use. Among high-school students, program participation was related to a lower likelihood of alcohol use. After-school programs are designed to reduce risk factors and increase protective factors for substance use, while providing youth with fun and social activities in a supervised environment. Summer programs include substance-use prevention messages in leadership and team-building activities while enhancing youth-adult partnership and mutual trust. Extracurricular clubs focus on helping youth resist drinking and driving. In order to examine the link between program participation and substance use, students indicating participation in one or more prevention activities were compared to nonparticipating students on self-reported drug use. Data were obtained from the Indiana Alcohol, Tobacco, and Other Drug Use Survey conducted by the Indiana Prevention Resource Center at Indiana University in the spring of 2004. A total of 98,442 students in grades 6 through 12 from 296 public and nonpublic schools participated in the survey; 91,331 (92.7 percent) were included in the data analyses. Information was obtained on the monthly use of gateway drugs and participation in any form of prevention activities. 3 tables and 17 references