I read it when I was 13 and babysitting for some hippies. I learned how to masturbate from that book LOL.
The book I got for my kids is Changing Bodies, Changing Lives which is very similar but for teens. My daughter (who is an adult now) said she learned a ton from it.
I really like this one:
http://www.amazon.com/Changing-Bodies-Lives-Expanded-Relationships/dp/081292990X/