Is he bored with school work? That was a HUGE problem for me when I was younger. My dad used to teach me more advanced topics, so I would want to learn them because it was a "challenge." For example, we would compete against each other doing timed tests like all the multiplication tables...100 problems in 5 minutes. I can make one up for you if you'd like.

Does he like to read? I think when I was that age I read the whole "Goosebumps" series of books. You could also try maybe doing some "Stories with a Hole" which you would read him a story, but there's a part missing out of it, which he would have to figure out. You can ask questions but they have to be Yes/No questions only.

I give you kudos for actually caring enough, that you want to help your son. Most people don't even try (somehow it was ok to have ADD, but when my Bipolar kicked in my parents didn't even want to acknowledge it).

If I think of more ways I'll let you know. Good Luck!