The Add Health core in-home sample consisted of 12, students who completed in-school and in-home surveys at wave 1. Members of this sample completed a second in-home survey 9 to 18 months later at wave 2. Adolescents were most likely to perceive maternal disapproval if their mothers reported strong disapproval and if they reported being highly connected to their mothers. Numerous psychosocial theories of health behavior, 5 , 6 as well as previous empirical research, 7 , 8 suggest that the timing of first sexual intercourse is influenced by a broad array of socioenvironmental and personal factors. Among the most powerful sources of social influence are parents, siblings, sexual partners, and friends.

Half of all mothers of sexually active teenagers mistakenly believe that their children are still virgins, according to a report released here today by a team of researchers at the University of Minnesota Adolescent Health Center. Teenagers, meanwhile, are under illusions of their own: 45 percent of boys, and 30 percent of girls, whose mothers say they ''strongly disapprove'' of teenage sex did not describe their mothers' outlook on the subject accurately. The finding that half the mothers whose teenagers are having sex do not know it was described by one of the authors, Robert Blum, director of the Adolescent Health Center, as stunning. Blum said the study did not examine why so many mothers were unaware of their children's sexual activity. We just don't know. The research also found that the mother's frequency of religious observance and prayer had no correlation with whether her children became sexually active.

September 5, Moms and dads everywhere, take heed. When it comes to sex education, and whether adolescents become sexually active, parental guidance is most influential when it delivered with warmth, openness, and ongoing effort. And to the surprise of many parents, such efforts are welcomed.

Advice columnist Carolyn Hax answers a letter about a mom with a sexually active teenage son. Now they are 16 and 17 and have girlfriends. The year-old is having sex and wants me to allow his year-old girlfriend to spend the night.