First you have him evaluated by a trained psychologist and/or physician to rule out attention deficit disorder, or some other problem. If no psychological or physical (meaning "brain") problem can be found, then I suggest you try finding him a teacher who is strict, fair, and will challege him. He may just be bored. There are huge differences in school experiences based on the teacher the child has. There are very good and very bad teachers, although most are somewhere in between. Your child needs a very good teacher! And you have the right to ask for one (although many parents don't realize this).
Suplement his education at home with good books. No TV in the bedroom! No video games in the bedroom. If possible, unclutter his room, so that all there is to do in there is read or sleep.
I do not believe that hitting a child is a good idea. It may teach them to be afraid of you, but that's about it.