OK, I saw a part of the movie on TV but I think the title was wrong and I can't find it no.
In this movie, a kid with long blond hair has some psychopath thoughts, he killed a classmate because he made fun of him, he was wearing a mask when killing him. In the meantime his mother was called to the school because they were noticing that weird behavior. I think the movie was film in late 70's or early 80's
Thaks

Sounds like the first half of Rob Zombie's Halloween. It wasn't made in the time you mentioned, but it was set then and parts of it had that feel.