To examine the long-term effects of an intervention combining teacher training, parent education, and social competence training for children during the elementary grades on adolescent health-risk behaviors at age 18 years. Nonrandomized controlled trial with follow-up 6 years after intervention. Public elementary schools serving high-crime areas in Seattle, Wash. Of the fifth-grade students enrolled in participating schools, 643 (76%) were given written parental consent for the longitudinal study and 598 (93%) were followed up and interviewed at age 18 years. A full intervention provided in grades 1 through 6 of 5 days of in-service training for teachers each intervention year, developmentally appropriate parenting classes offered to parents when children were in grades 1 through 3 and 5 through 6, and developmentally adjusted social competence training for children in grades 1 and 6. A late intervention, provided in grades 5 and 6 only, paralleled the full intervention at these grades. Self-reported violent and nonviolent crime, substance use, sexual activity, pregnancy, bonding to school, school achievement, grade repetition and school dropout, suspension and/or expulsion, and school misbehavior; delinquency charges from court records; grade point average; California Achievement Test scores: and disciplinary action reports from school records. Fewer students receiving full intervention than control students reported violent delinquent acts (48.3% vs 59.7%; P=.04), heavy drinking (15.4% vs 25.6%; P=.04), sexual intercourse (72.1% vs 83.0%; P=.02), having multiple sex partners (49.7% vs 61.5%; P=.04), and pregnancy or causing pregnancy (17.1% vs 26.4%; P=.06) by age 18 years. The full intervention student group reported more commitment (P=.03) and attachment (P=.006) to school, better academic achievement (P=.01), and less school misbehavior (P=.02) than control students. Late intervention in grades 5 and 6 only did not significantly affect health-risk behaviors in adolescence. A package of interventions with teachers, parents, and children provided throughout the elementary grades can have enduring effects in reducing violent behavior, heavy drinking, and sexual intercourse by age 18 years among multiethnic urban children. Results are consistent with the theoretical model guiding the intervention and support efforts to reduce health-risk behaviors through universal interventions in selected communities or schools serving high-crime neighborhoods.