Apologies for derailing that other thread, and thanks to the Mods for pointing that out.
As I mentioned over there, we had sex ed. classes, to varying degrees of content, in middle school and high school. The middle school version was taught by the science teacher, and it was very by the book, more like an anatomy class.
In high school, the split up the boys and girls into separate groups, and, as I recall, they had classes for one period for a week. It covered a lot of information, both anatomy, STD prevention, condom use, the reproductive cycle, and the like. The teacher who led the class was very warm and sympathetic, and that helped.
I also benefited from the fact that my mom and I had several frank discussions on these topics when I was [I don't think if I can mention my age here]. I was the youngest of four kids and the only girl, so I guess my mom thought this was "her moment." It was hugely beneficial to me, both in terms of information and emotional preparedness, and I think I was better informed than most of my peers.
In fact, when the moment arrived, I can honestly say that I made the decision with full freedom and full willingness. I chose to do it, and I wanted to do it. Of course, even though our discussions were long and thorough, there were some details she left out, and I had to discover those -- much to my surprise -- on my own.