The study found that academic achievement and parental monitoring protected adolescent boys from early sexual intercourse and risky sexual behaviors. Risk factors that made early sexual intercourse and risky sexual behaviors more likely were drug and alcohol use and school problems. The protective factors were found to have an indirect effect on the risk factors, in that parental monitoring and academic achievement were linked to a reduction in adolescents' drug and alcohol use and school behavioral problems. Approximately 30 percent of the adolescent boys engaged in sexual intercourse by age 15. The average age of sexual debut was just over 12 years old. Of these sexually active boys, just over half engaged in unprotected sex with multiple partners. These findings show the importance of initiating intervention and prevention programs before middle school or high school. The domains for such programs should be the family and the school. Data for this study were drawn from the first and second waves of the survey component of the Welfare, Children, and Families: A Three-City Study. This is a household-based, multimethod, longitudinal study that consists of survey, observational, and direct-assessment data. A sample of over 2,000 low-income children and their mothers in low-income neighborhoods were stratified and randomly selected in Boston, Chicago, and San Antonio in 1999. Of the eligible households, interviewers selected one focal child to participate in interviews, along with their mothers. The analyses focused on households with a male focal child age 10-14 years old at Wave 1 in 1999 and who also participated in Wave 2 in 2001 (n=528). 3 tables and 69 references