Your son most likely does not have ADHD, this misdiagnosis gets thrown around a lot these days to the extent that 20% of boys are diagnosed by the time they are through high school.

From the article

http://www.esquire.com/features/drugging-of-the-american-boy-0414?utm_source=pocket&utm_medium=email&utm_campaign=pockethits

but what's happened is, particularly in schools where most of the teachers are women, there's been a general girlification of elementary school, where any kind of disruptive behavior is sinful. What I call the 'moral diagnosis' gets made: You're bad. Now go get a doctor and get on medication so you'll be good. And that's a real perversion of what ought to happen. Most boys are naturally more restless than most girls, and I would say that's good. But schools want these little goody-goodies who sit still and do what they're told—these robots—and that's just not who boys are."