Math, History, reading and writing are factual. Sexual education can be taught from a secular point of view or a christian point of view. I will teach my kid the right way. I pay taxes so that my kid can get an education that will prepare him for college. Not so he can have some 40 year old man teach him how to use a condom.
I'm glad your kid is fortunate enough to have a parent who can teach him/her the ways of the world. Others aren't so lucky. Many find out for themselves, the hard way. By promoting sexual education in schools WITH AN OPT-OUT OPTION for parents who wish to educate their children themselves, it doesn't need to be that way.