Taught early in high school: How to do sex, in real life. Not STI education, not pregnancy/fertility, not how to be safe, or the biology of penises and vagines. How to go into sex and do it so that it's fun and feels good, how to listen to your body and your partner, maybe how to attract the opposite sex, and so on. Dunno about elsewhere, but in the US guys get all their sex education from porn, and girls used to get none at all. (now... also porn?) Porn is fun, but it's Kabuki Sex, and it only vaguely relates to real-life sex. It'd be like giving a 16-year-old a driver's licence when the entirety of his/her driving education consisted of watch Hollywood Car Chase movies.

Of everything useful I ever learned about sex, 50% of it was from Dan Savage and 50% of it was from my fiance, both many years after I had actually started trying to do sex on my own. This is stupid.