Sex Education
 

Teaching the birds & bees seems to be extremely embarrassing and difficult for many parents. Chances of them being taught anything in school is slim to none these days. So if you break out in a cold sweat thinking about it, at least buy the kid a book.

Sex education here starts at age 5-6 (that's just the correct naming of the parts though).
It continues in age appropriate fashion all the way through school.
Parents can opt out, but when I was working in school that was only two children - one from a Muslim family, one from a very strict Christian family.

Religion = not thinking FSM invented anything that goes in your pants except the parts that make pee-pee.