The best sex education for high school age children is hygienic. They really benefit by learning a great deal about venereal diseases.
This works on the same principle that at a certain point in their training, pre-med students develop Microbiophobia, after learning of the pervasive nature of microorganisms. For a while, they tend to be very conscious of contamination and cleanliness.
Importantly, this is not the same as advocating condoms, because many forms of VD are not avoided with their use. But optimally, becoming aware of VD will make them a bit more standoffish, which is not a bad thing at that age.
“I really love you, but until we can show each other medical tests that we don’t have VD, we had better not, you know...”
And since the information is valid, it serves them for the rest of their lives, helping them to spot symptoms.
They're talking about 5 year olds here, not high schoolers.
The best sex ed a kid that age needs is to know that boys/girls have cooties. STAY AWAY!!!