School has limited influence on kids when compared to parents. If your parents don't see casual sex as a big deal, neither will you. If your mom got pregnant at 14, well, I guess it's not a big deal if you get pregnant at 14 either.

I grew up in a fairly wealthy little town where pretty much nobody was the child of a teen parent. It’s awfully facile, and to my own experience, to pretend the children of such parents are the only people having sex in high school.

I live in a part of Maryland with high teen pregnancy rates. Unsurprisingly, the pregnant teens are often the children of single moms who were also pregnant teens. Is this a coincidence? Even ignoring truancy problem, somehow I don't believe sending all these kids to wealthy gold-plated schools to get a "proper" sexual health education will fix the issue because my argument is that the messaging they receive at home through their parent(s) is 10x stronger and more influential than the school's messaging.

I would guess failure to use effective birth control methods could be correlated pretty well with income but I’d be pretty surprised to see any evidence that sexual activity was much lower in the tony towns. I’m also going to refer back to my memories of being a teenager to say that I often didn’t really put much stock in my parents’ values or wisdom, and hardly think I was alone in this.

Anecdotal evidence

Do you think I’m wrong to say that sex education courses, regardless of whether they’re abstinence-only or more modern, typically already include admonitions against promiscuous sex?

No, you are not wrong to say that... but that’s not what your parent comment was saying. Your comment was saying that messaging did not have much influence on your behavior later in life. I’m saying that just because it didn’t have much influence on your behavior does not mean it hasn’t had much influence on the behavior of others

Well, if it’s widespread, and yet people are not behaving as we would wish, I would conclude it’s not very effective at influencing their behavior.

You do not know that the problem wouldn’t be worse without widespread messaging.

That's impossible to prove or disprove. Fortunately we don't have to because it's been well demonstrated that it's not sufficient.