Which sex ed approach works best for STI and pregnancy prevention? Research remains unclear

And that’s the crux of the problem. There have been so few well-designed studies that tell us if sex ed is helping, making things worse or doing nothing at all. Researchers would have to randomly assign preteens or teens to a sex ed class and then figure out how to monitor subsequent unwanted pregnancies and sexually transmitted infections. Students don’t always disclose the truth about sex on surveys.

“It’s really challenging to do an evaluation of sex ed curriculum,” said Carolyn Tucker Halpern, chair of the department of maternal and child health at the Gillings School of Global Public Health of the University of North Carolina at Chapel Hill. “Short of rummaging around in trash cans and looking for used condoms and stuff, it’s hard to get an objective measure.”

The most recent attempt to compile and summarize the best evidence for sex education was published in 2023 by a team of public health researchers from Dartmouth College. They aggregated the results of 29 randomized controlled trials (RCTs) in the United States between 1990 and 2021. Fewer than half of the studies of sex ed programs took place in schools. Nine of them emphasized abstinence, which means waiting until marriage to have sex. Just one study directly compared teaching abstinence only with a comprehensive approach. (It did not find any difference in frequency of condom use, its main outcome measure.)

Comprehensive sex education is a catchall term that includes everything that isn’t abstinence only – from birth control use and sexual consent to the reproductive system and sexually transmitted infections. Comprehensive programs may also include or even emphasize abstinence along with these other topics. Because the content of these classes varies, it’s hard to generalize about comprehensive sex or its effectiveness. (For more on current approaches to sex education, read this Hechinger Report story.)

Only seven studies in the Dartmouth meta-analysis attempted to track pregnancies, and of those, just three asked participants whether they or their partner had gotten pregnant a year or more later. 

The overall finding was ambiguous. Three comprehensive programs showed a moderate reduction in teenage pregnancies although the effect was not statistically significant. This means that there are too few studies for researchers to be confident; the results could be flukes and more studies are needed to confirm. (The largest of the three studies, by far, involved young men who were living in group homes operated by child welfare or juvenile justice, not indicative of typical teens.)

There was also no evidence that sex ed decreased the incidence of sexually transmitted infections. Only three studies in this 2023 meta-analysis tracked STIs (not the same as the ones that tracked pregnancies) and all three showed similar rates in both the treatment and control groups. It’s hard to make confident conclusions based on only three studies, but these results are not promising.

“There’s a shockingly low number of studies,” said Amy Bordogna, who led the research team that conducted this review, published in the American Journal of Sexuality Education. “There needs to be more research.”

The 29 randomized controlled trials tended to show that students were practicing safer sex after participating in a sex ed program. On surveys, for example, boys said they were using a condom more often. In theory, increased condom use should be translating into lower pregnancy and STI rates. Either teens aren’t being truthful on surveys or the condoms aren’t being used correctly.

The rigorous research evidence is at odds with the research-based recommendations of many medical and health associations, including the American Public Health Association, the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. Other reviews have found that the evidence for “comprehensive” sex ed programs is more favorable. For example, a 2012 paper by 20 experts, led by researchers at the Centers for Disease Control and Prevention, reviewed 66 studies of group-based “comprehensive risk reduction” programs and concluded that, on average, they were effective in reducing pregnancies and STIs, while the results of 23 studies of group-based abstinence programs were inconsistent. Many of the underlying studies included in these broader research reviews weren’t randomized controlled trials and were of lower quality. 

Advocates on both sides of the debate tend to overstate their cases. There’s little evidence that sex education encourages sexual activity or promiscuity, but there’s also not strong evidence that comprehensive sex ed programs reduce pregnancies and infections. 

There’s also little evidence that abstinence-only approaches backfire, as some suggest, and lead to higher rates of pregnancies and infections. A 2008 study of four abstinence-only programs found no increase in the risk of adolescent pregnancy, STIs, or the rates of adolescent sexual activity compared with students in a control group.

The international evidence isn’t much better. A Cochrane review published in 2016 aggregated the results of randomized control trials that took place in schools in Europe, Latin America and Africa. The review had a higher bar for study quality; there had to be some clinical measure of pregnancies and sexually transmitted infections beyond what students voluntarily disclosed. It found no evidence that school-based sex ed programs by themselves reduced pregnancies, HIV or other sexually transmitted infections after reviewing eight randomized controlled trials covering 55,000 students.

One takeaway from the lead researcher, Amanda Mason-Jones from the University of York in England, is that a curriculum alone, unaccompanied by freely available birth control, isn’t terribly effective. 

The most effective way to reduce pregnancies had nothing to do with sex ed classes. Financial incentives, such as free uniforms or small cash payments to keep girls in school, led to a significant reduction in teen pregnancies. One of these studies also documented a reduction in infections. That suggests that education itself might be the strongest form of birth control.

Sarah Butrymowicz contributed reporting to this story.