In the tipsy-topsy world we live in, this is known as a "controversial" idea. Unlike, say, alternative visions of human sexuality -- such as that it is empowering for young women to have sexual adventures outside of marriage, so long as they use condoms.
Thanks to a really interesting database called the National Longitudinal Study of Adolescent Health, researchers have been able to track the effects of virginity pledges on teens' actual sexual behavior.
The first batch of research (by Peter Bearman and Hannah Bruckner) was released in 2001. Looking at a nationally representative sample of teens age 12 to 18, the researchers concluded that pledges work. Teens who take them delay sex on average an extra year and a half.
"The delay effect is substantial and almost impossible to erase," the researchers note. However, the pledge worked because it created an "identity movement," a "moral community" that is effective only if the group was not too small and also not too large. (If everyone pledges, then the pledge is no longer a distinctive badge of moral identity.)
Other interesting findings: Clear, explicit parental disapproval of sex also helped teens, including older teens, avoid sex: "Perceived parental disapproval of sex, however, is a strongly delaying factor throughout adolescents."
In general, the more connections and activities the teens had, the less likely they were to have sex. With one exception: "The more frequently and the earlier adolescents date, the earlier they have intercourse." If you don't want your teens having sex, tell them so. Tell them why. And delay the onset of the dating game.
In an update released last month (the teens are now 18 to 24 years old), the same researchers focused on the trouble with pledges. They are not a miracle cure. Most pledgers eventually have nonmarital sex. While their rates of sexually transmitted diseases were slightly lower, the difference between pledgers and nonpledgers was not statistically significant -- even though pledgers reported significantly fewer total sexual partners than nonpledgers. Apparently they use condoms and seek medical care for STDs less often.
Maggie Gallagher is a nationally syndicated columnist, a leading voice in the new marriage movement and co-author of The Case for Marriage: Why Married People Are Happier, Healthier, and Better Off Financially.