As someone who went to a liberal private school and was STILL pretty clueless, I really doubt most kids get enough in the way of sex ed.
To be fair, I knew about menstruation, and safe sex practices, and the basics of PIV intercourse, but...I don't think that's really enough. I lost my virginity relatively late (20-ish) and still, at the time, knew virtually nothing about my own body. My mom had given me books to read when I was younger that had given me some idea about the clitoris, G-spot, etc, but I didn't really get it. And since I had masturbated when I was younger, but never to orgasm, so I didn't think I was really missing out on much; I thought female orgasms were these rare, magical things that could only be achieved through partner sex. It wasn't until a friend finally told me about her experience with vibrators that I started to look around online.
I know from having talked to other women that my experience is not unique; there is so little emphasis placed on female anatomy and sexuality, and I think it's a shame--even a sign that something is wrong--that so many girls start having partner sex before they know anything about pleasing themselves.