Pop Quiz:

1) Does comprehensive sex education encourage teens to have sex?

2) Does abstinence-only education discourage teens from using protection?

If you answered "Yes" to either of these questions, you probably know less about sex education than you think. These two bits of debatable conventional wisdom used to have some evidence backing them up. But the newest and most trustworthy research shows they're wrong. Comprehensive sex ed actually delays loss of virginity in many cases. And kids who've taken abstinence ed classes aren't any less likely to use condoms than their peers who didn't take the classes.

A lot has changed in the 11 years since Congress voted to make abstinence-only programs eligible for federal funding. Today, that policy is up for reevaluation and a bill aimed at opening the funds to comprehensive programs will likely be put to a vote sometime in 2008. Before you decide where you stand, maybe it's time you got up to date on the research.

First off, there are many peer-reviewed, published, randomized studies showing that comprehensive sex ed—which emphasizes abstinence and also provides safer sex information—might  work. There is far less such evidence supporting abstinence-only programs. But that doesn't mean we can discount abstinence-only entirely. The specific program matters a lot. Fact is, with either abstinence-only or comprehensive, some programs work and some don't.

Why so much ambiguity? According to leading researchers, sex education is a difficult field to study and few people get it right. "The vast majority of the research, whether it favors abstinence or comprehensive, is so poorly done that the results mean nothing," says Dr. Douglas Kirby, senior research scientist with ETR Associates, a nonprofit organization that publishes materials on a wide variety of health topics, including comprehensive sex education.

Kirby, who has researched sex education for more than three decades, has spent the last 10 years trying to solve the problem of inadequate research. Since 1997, he's authored four massive papers looking at the few studies that are credible and trying to find patterns of evidence that point toward a solid answer—research he says favors the comprehensive approach. His most recent report, Emerging Answers 2007, dealt with studies surrounding 48 comprehensive programs. Of those, 40 percent delayed the initiation of sex, reduced the number of partners for sexually active teens, and increased condom or contraceptive use. He says there isn't much evidence that the abstinence programs he looked at did any of those things.

Dr. Stan Weed, director  of the nonprofit Institute for Research and Evaluation, which specializes in researching and advising abstinence programs and policy, disagrees. Weed also has several decades of experience under his belt, and his  findings—like Kirby’s—are respected in government and academic circles. Weed and his staff have conducted at least 100 studies over the last 15 years, and he says his research shows that the well-designed and well-implemented abstinence programs do delay sex, reduce partners, and prompt teens who've had sex in the past to stop. In fact, a recently published study he conducted of a program in Virginia showed a 50 percent reduction in teens having sex for the first time, when compared to teens who had no significant sex education.