I'm trying to find a manga where the main character is a boy with no aptitude for magic, but wants to learn magic. He goes to a magic school despite the fact that he can't do.
His teacher looks like a magician but in reality is a fighter and has muscles. The main character one-shots the Demon Lord (who looks like a skeleton) and later there's more Demon Lords of Earth and Lightning
It turns out that the main character is very powerful, so whenever he uses a wand it breaks in half.