School’s back! To celebrate, FiveThirtyEight’s science crew figured it was time to talk about sex. Sex ed, that is. Over the next few days, we’ll be discussing why sex education is such a flashpoint and what role science can play in figuring out what kind of sex ed kids should get.

Debates over how (and even whether) sex ed should be taught in schools have raged for more than a century, with no end in sight. Those debates are fought on both scientific and cultural grounds — they’re about what works to prevent teen pregnancies and STDs and what’s appropriate for American kids to be taught in school, and at what age they should learn it.

The latter questions are important — and also outside the scope of science. They’re rooted in values, not evidence. We can answer the more concrete questions, though. What do we know works about sex ed? And what does it mean for something to “work” in the first place?

Hundreds of studies on sex ed and teen pregnancy prevention programs have been conducted, and what they show is that teaching kids about sex doesn’t make them start breeding like rabbits. Instead, it may prod them to delay having sex. Comprehensive sex education programs that include information about contraception have also been shown to reduce rates of teen pregnancy and sexually transmitted diseases and to increase the use of condoms and other contraceptives.

Those are the broad lessons. Where it gets messy is when you try to tease out which programs work best. Read more via FiveThirtyEight