The numbers can tell us what is happening but not why. We can speculate, though, on the basis of interviews with both high school and college samples. In the past, boy’s first sexual experiences were often with marginalized girls, young women with “bad reputations,” sometimes unfortunately called “sluts.” The teen culture’s sexism allowed boys the freedom for more sexual experiences at younger ages than girls, with little risk of social stigma.
Not anymore. Now, teenage girls are as likely as boys to presume that “being in a relationship” involves being sexually active. Boys are likely to start their sex lives with girlfriends.
An additional benefit is that relationship sex is more
likely to be responsible than casual sex. The rates of STDs, unplanned pregnancies, and abortions have also dropped dramatically among teens. Teens are not having less sex, but they are more responsible.
By 1997, adolescent males and females resembled
one another in sexual activity

Source: author's tabulations from Youth Risk Behavior Surveys.
This study appeared in the inaugural issue of Context, the American Sociological Association's new journal for non-specialists and the public.
Barbara Risman, Professor of Sociology