But when I went to college I had the same issues. I have a degree in Bio Engineering and receive A's and B's in advanced classes but had to take Biology 3 times to pass it.
He most likely thinks about things much differently then most people do. His mind will often wander unless he is solving a problem that most people would need a calculator for but he can do this without paper or a calculator.
These are my experiences and I have a similar IQ.
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.