I would say if there's any suspicion, have him fully and properly evaluated. There's nothing worse than feeling abnormal, dumb and like a failure when at the same time parents and teachers are telling you that you're smart, or worse, an underachiever. You begin to distrust them all and feel hopelessly alienated because nobody is on your side.
ADHD is insidious. I wasn't diagnosed until my 30s. Being unconscious of it was an awful burden for all those years. You go from telling yourself "I'm a failure. I'm smart but I'm stupid" to "That's why I failed. I'm smart but my brain has problems performing certain functions."
I think that's my most important point: You and he and the teachers must become conscious of it if he has it. Then when the going gets rough you know where to point the finger and where to focus the energy finding solutions. Then he won't blame himself and they won't blame him.
Diet and exercise do help mightily, but remember that medications don't have to be an all-or-nothing situation. I do best on very small as-needed doses. A couple of mg of a non-extended release stimulant, for instance, can work wonders to calm the mind, turn off the noise, and aid focus. It's in an out of the system in just a few hours.
One thing I was not conscious of was the anxiety that ADHD produced by me having to constantly control my impulses to simply get up and get the heck out of dodge. No, I don't want to sit still; no, I don't want to look at people when they talk; no I don't want to act all calm, but I have to do all these things to be socially acceptable. It's like a thousand cuts having to suppress that all the time. This is where meds, diet, and coping techniques can help greatly, but one has to first become acutely self-aware of these otherwise unconscious, instinctive realities.
