Teaching children about sex is not the governments job.
You don't think a very basic and necessary biological function should be taught in school?
No, it should not. That is why we have parents.
Unfortunately, parents in this nation have been largely absent from their basic roles and jobs so sex education has essentially been forced into the schools. The children need to get the information from somewhere and the schools are it because the parents have failed to do so.
The problem, of course, is that 'sex' is only a small part of what they want to teach in sex education. 'Alternative lifestyles' and the like are lauded as sex education and this is where you start to get into problems when you leave parenting to the government.
At one time my sister came home near tears because the school was telling the kids that broken homes were so much better than complete families. There was a list of all the wonderful things that children get when they have 2 homes rather than one. Asinine in the extreme but, again, when you expect the state to parent this is what you get.
Is there a good solution? Not really - we can no longer expect parents to step in so we cannot eliminate sex and other 'moralistic' education to be removed from the schools but they do a an extremely shitty job at it.