A new data analysis of in-school condom distribution programs from the 1990s has added new complexity to our understanding of teen pregnancy prevention. Most previous studies have shown that access to free contraception decreases teen birth rates, but this is the first robust study of condom-only programs. Researchers Kasey Buckles and Daniel Hungerman of the University of Notre Dame found that teen births rose 10 percent at schools that gave out free condoms to students.

The study distinguished between schools with free condoms that provided mandatory counseling about proper condom use and schools that gave out the condoms with no instruction. The authors tracked pregnancy rates before and after the condom programs were introduced in each school, and they compared these numbers to the pregnancy rates at schools that had no condom program at all and the pregnancy rates among young women aged 20 to 24 in the same areas as the school. This allowed them to control for the possibility that broader societal shifts were driving the rising pregnancy rates in the schools that offered free condoms.

Unsurprisingly, the 10 percent increase among condom-distributing schools was mostly caused by schools that did not give their students mandatory counseling about how to properly use condoms. Schools that did provide counseling “may have seen no change or perhaps a decline” in teen birth rates, according to the study’s authors. Condoms might seem simple, but about 18 out of every 100 regular condom users get pregnant each year, mostly due to spotty or incorrect use. A study of male college students found that 40 percent had not left space at the tip of a condom at least once in the previous three months; 15 percent had removed a condom before finishing sex. High school students without any counseling on proper use probably wouldn’t fare much better.

There are a few possible explanations for the increase in teen birth rates at schools that gave out condoms with no instruction. Teens might have been too shy to buy condoms but reluctant to have sex without them, so they had sex more often than they would have without free access to condoms. This seems less likely, since at least one study has found that school free-condom programs increase condom use but don’t change frequency of vaginal intercourse or attitudes toward sex.

It’s also possible that the teens in the 10 percent increase zone used condoms, the best protection against STIs, instead of oral contraceptives or long-acting reversible contraception (LARCs), like IUDs and implants. Pills and LARCs are far more effective at preventing pregnancy than condoms (a Colorado initiative that provided teens with free LARCs cut the state’s teen birth and abortion rates nearly in half), but they require a visit to the doctor, which might be a hard ask for a teen who can’t or won’t talk to her parents about sex.

The study’s authors posit a third explanation for the change in teen birth rates: Staff at the condom-distributing schools that did not offer mandatory counseling may have seen the condom program as a substitute for education. “Programs without mandated counseling thus may have created a moral hazard problem in that they unintentionally disincentivized school personnel from promoting contraceptive use or other conduct discouraging conception,” the authors write. School officials may have felt that they’d already done their part to prevent teen pregnancy and didn’t feel the need to expend any more time or resources on pregnancy prevention initiatives or contraception education.

This new research offers another bit of evidence that promoting teen sexual and reproductive health requires a both and solution, not an either or. Teens need condoms to prevent STIs, and they need a wide variety of contraception options to suit their needs. But without comprehensive sex education, the benefits of both will be limited.