That is a very strange take, I'm sorry to say. Really strange. On both counts.
I don't know what the answer is, but it's certainly not like we had a public school teacher sex control system 40 years ago and forgot. There are tons of good and bad factors that play into it. You can certainly find examples of school systems where it's not happening, and others where it is. To me, it doesn't seem to follow any sort of pattern that prejudice might tell us to look for.
Now, 100 years ago, yes. We really did have good controls around sex 100 years ago. Seriously.