"going to school and paying attention but being taught that abstinence is the only effective form of birth control and that condoms fail regularly so why bother" All so parents don't have to deal with the horror-movie scenario of their adolescent kids having a responsible, happy sex life.
I think there are a lot of good points being made, but you guys may be caught up in the math and are forgetting something fairly simple.
Sex is free, fun, and easy. The less education you have the less likely you are to understand effective birth control. The less wealthy you are the less you have to spend on contraception. Those things together with the easiest and cheapest form of entertainment would seem to cirrelate with a higher birthrate in lower income brackets.
I cant find any studies that support what Im saying right now, but the logic holds.
Sure we could come up with a bunch of reasons each way. They're probably all wrong. But why are we speculating? Just go ask some rich people why they want/don't want X number of children and they will tell you.
There's also the whole "not being aware contraception exists because you couldn't go to school" thing.