I disagree with using physical means for discipline. There are already too many issues where kids don't use their words and instead act out, a parent doing the same thing just exacerbates the situation. They're the ones that (typically) end up getting into fights, and doing the same to their kids. Anyway, enough of that.
Have you thought since your child always got straight A's and seems to know the stuff so well that he's just bored? That whole "not being challenged enough" thing can be true. Are there any GATE programs or anything at this school? Something that may be more fun so that it challenges him?