Children differ in their development. A good parent will know when their children are ready for sex education. The children will start to ask questions and their questions will be answered truthfully and only answering what the child has asked and can deal with at that time. Sex education from parents should be built up gradually, usually as dictated by the child.
Unfortunately there are some parents who just won't bother, so I suppose schools have to take over, but as a parent I would thoroughly oppose my young child receiving sex education before they are ready to understand it properly.
So basically, I agree with RI Geezer and entirely with flip flop and I don't see why we should have to accept sex education in schools because some parents can't be bothered about their kids.
Schools, in my opinion, are their to give my children an education in the basics, parents should do the rest. We need to get back to a society with proper parenting.