There's an argument for ADHD being over-diagnosed, but your sentiment trivializes the issues that can prevent people like me from attaining a better quality of life. I was about 23 by the time I got treated for ADHD. I often wonder how different my trajectory as an adult might have been had I been treated while I was still in high school. I got abysmal grades -- just barely graduating, in fact -- and I dropped out of college rather quickly. I beat myself up on account of my failures, over which in hindsight I had very little control.

Amphetamines are no panacea. I don't truly know what I'm doing to my heart and brain in the long term, anorexia is a constant concern, and coming down from what I would describe as a 6-hour high can be devastating to my mood, but they overall they improved my quality of life and facilitated me attaining a career as a software developer. Perhaps more exercise would be just as effective as a treatment, but knowing that I had a legitimate problem was crucial.

The majority of "young boys" do not have ADHD, and "physical activity" is far more general than "recess".