There's a pretty broad spectrum of what ADHD means - could be more lacking attention, could be more hyperactive activity. And there are coping skills that kids can learn and accommodations that schools will make to help him continue to be successful. Since you mention testing - ADHD doesn't mean the kid is less intelligent. It just means he struggles to pay attention at times.

Check out CHADD - they've got some decent resources. Or at least they have in the past - I haven't looked over their stuff for a while, but I assume it's still good.