As a teen in 2015, it’s possible to graduate from high school knowing how to solve calculus equations but have zero clue how your penis or vagina really works.

Why? Because sex education—public school instruction on how all the parts function—in America is bad. So bad it’s almost a joke, or at least a funny enough punchline to merit a 20-minute sketch on a late night talk show.

In his recent condemnation of American sex ed protocol (or the lack thereof), Last Week Tonight host John Oliver offered an entertaining rundown of some of the worst aspects of our system, from the cringeworthy films students are forced to watch to the judgmental nature of some lesson plans.

But how does this flawed system impact actual teens, beyond the trauma of hearing your gym teacher discuss genital warts? Curious whether there might be a correlation between what’s taught and teen birth and STD rates, I broke America’s sex ed laws down by state. And while sex ed isn’t the only thing that affects these rates, the maps show some pretty clear patterns.

First off, sex education in this country is wildly inconsistent. Some states—like New York, Oregon, and Maine—require sex ed as a graduation requirement and require that sex ed classes include information on condoms and contraception. Think of those states as the ideal. On the other end of the spectrum, states like Texas, Oklahoma, and most of the middle of the country don’t require sex ed to graduate. The middle ground includes states that either require sex ed to graduate and don’t require condom instruction, or states that don’t require sex ed but do require a lesson on birth control when it is taught.

Confused? That’s because America’s sex ed framework is a total mess. Even within states that don’t require sex ed, individual districts can choose to offer the coursework. No states outright ban it, but most leave it up to local officials.

Take Alabama, which doesn’t require sex ed but does require contraception instruction when sex ed is taught. As Christina Clark, a policy and training coordinator with the Alabama Campaign to Prevent Teen Pregnancy, explained to me, the street a teen lives on determines whether or not he or she takes a sex ed class. And figuring out which teens are (or aren’t) taking sex ed is nearly impossible.

“We don’t have a mandated sex ed law, so a lot of young people in Alabama aren’t getting sex education,” Clark said. “Because it’s not mandated, there are no tracking tools about who’s teaching and who’s not.”

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That the American sex ed system is patchy and abysmal isn’t new information. There are countless stories and investigations that illustrate just how bad it all is. Why devote more time to lamenting this reality? With all other outlets teens can utilize to get information about sex, does sex ed really even matter very much?

Simply put, yes. Good sex ed serves as a kind of equalizer. It used to be hard to show a correlation between teen behavior and sex ed curricula. But thanks to the Office of Adolescent Health and its countless investigations into how specific lesson plans affect teen sex habits, we now know that a thorough sex ed class can definitely play a part in how teens approach early sexual encounters.

Some curricula are proven to increase the odds that a teen will use a condom the first time he or she has sex. And when more teens either delay sex or use a condom, a state’s teen birth rate often drops.

Omar Bustamante/FUSION

As you can see, states like Texas, Louisiana, Oklahoma, and Arkansas don’t require sex ed, and—surprise!—they have some of the highest teen birth rates in the country. Meanwhile, New Jersey and Vermont require both sex ed and contraception instruction, and they boast some of the lowest teen birth rates. There are outliers (see New Mexico), but experts say the association cannot be ignored.

Teen birth rates across the board are way down from their peak of 61.8 in 1991 to 26.5 in 2013, the most recent data we have available. As Bill Albert, chief program officer for the National Campaign to Prevent Teen Pregnancy, told me, a few things have happened since 1991 that are theorized to play a part in the decline. The economy took a significant downward turn, MTV’s 16 and Pregnant premiered, and, last but not least, the federal government started investing millions of dollars in sex ed programs that actually work.

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Something else that happens when you get teens and young adults to use condoms and have safer sex is the spread of sexually transmitted disease starts to slow down. The most commonly reported STD in the U.S. is chlamydia. It’s also the most common STD spread among adolescents.

But according to a spokesperson with the Centers for Disease Control, early surveillance data “show signs of potential progress in reducing chlamydia among young people aged 15 to 24.” The decline could be attributed to a number of factors, and the link between sex ed, contraception instruction, and disease rates is a bit looser. However, since chlamydia is spread during sex—unprotected sex—an increase in adolescent condom use can’t be discounted.

Omar Bustamante/FUSION

There are two big, highly-politicized buzzwords that get tossed around when talking about sex ed: “comprehensive” and “abstinence-only.” It’s commonly understood that a state, district, or school has to belong to one of these groups, but can’t belong to both. It’s also commonly understood that abstinence-only programs don’t work. But Albert told me it’s unfair to classify sex ed programs this way. The two terms aren’t mutually exclusive.

The term we should be using, he said, is “evidence-based.” The name comes from the federal government’s Teen Pregnancy Prevention initiative, and simply refers to a lesson plan that is evidenced to actually change teen behavior. Most of these programs teach both abstinence methods and birth control, which Albert told me is generally the best approach.

“The successful programs tend to talk about relationships and what healthy relationships are,” Albert said. “They talk about how it’s quite normal and okay to say, I’m not ready to have sex, but if you are having sex, here’s the information you need. Most 15-year-olds haven’t had sex, but most 17-year-olds have. You need to have both messages.”

A two- or three-year difference in age doesn’t mean much to people in their twenties and thirties, and means even less as you get older. But to 14 and 15-year-old freshman and sophomores, two years represents a huge gap in age politics and life experience. A good sex ed class—which, at many schools, students can take at any point—has to cater to both inexperienced-but-curious freshmen and slightly-experienced-but-still-curious upperclassmen.

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Public school sex ed is controversial because it involves giving people we’ve decided are too young to vote, too young to live alone, and too young, in some cases, to drive a car information about creating new human life. But just as aggressively telling kids not to have sex doesn’t stop many from doing it, providing them with accurate information doesn’t encourage them to start sleeping around, according to sex educators.

To use the “sex is like driving a car” metaphor: Before a teenager can get a license, he or she has to take a driver’s education class. In most of these classes, students watch videos of deadly accidents—a scare tactic to show new drivers the very real dangers of driving recklessly, without proper protection. Students are then given information on how to drive a car safely, on how to avoid the deadly accidents.

Sex ed classes that only teach the scare tactics—pain, pregnancy, deadly disease, undesirability—without providing positive information on how to navigate sex safely don’t work. Teens, unlike children, are smart enough to know when they’re being duped by authority figures. The scare tactics don’t keep teens from having sex with each other.

They just make it that much harder for them to do it safely.