Are they teaching abstinence "until you're out of high school"? Otherwise it's either "until marriage" or "until death." I think most kids understand that marriage usually involves sex, even with bad sex ed.

I think they're just teaching "until ..."—as in, they don't have an "until", it's just "don't have sex." As if sex was exactly equivalent to a drug, where if you avoid the particular subculture that "does" the drug, you'll just never need to think about it.

Though I think the true implication is "don't have sex until an impulse comes along to do so, that is strong enough to completely drown out the voice of your superego in your head. And then—if the impulse really is that strong—the 'proper' order to do things is to get married to that person, and then have sex with them."

I can't speak for others, but I was never taught the "until marriage" clause, and I graduated high school in 2011. We were taught that abstinence was the only way to completely remove the risk of pregnancy or STD/STI, which really doesn't change once you're married or whatever.

They do in the South.

And in the Midwest.