Son will be fine. Not telling anyone what to do but try non-medication alternatives first. Also try to minimize any documention or paperwork with your son's name on it and an ADHD diagnosis. Just no reason to create additional headaches.
I would avoid having him "diagnosed" and even seek a second opinion to squash the first "diagnosis". The second opinion could be "well, he exhibits some symptons, but he is not ADHD". "I recommend medications XYZ to address these sympton"
I would get the doctors opinion (Doctor-2) that he
does not have a
mental disorder but may be suffering from environmental induced factors (school, diet, etc) triggering "some" symptoms.
Write some "notes to self" notes regarding your conversations with doctor. Doctor may be able to write a "To Whom it May Concern" letter with a short paragraph that he examined your son on XXXX date, he does NOT have ADHD (at the time of exam) and he does NOT have any mental, emotional, or other disorders.
This is your get-out-of-jail letter, keep it on file.
This helps address the "Have you EVER, in YOUR LIFE, been
diagnosed with" medical problem on the 8500. (Item 18m)
http://www.leftseat.com/Programs/85008.htm
With that said, if he indeed has ADHD and indeed needs meds, I don't know what do say. The above advice is geared towards him being "on the fence" and assuming increased exercise, reduced sugars and white carbohydrates (bread, pasta, sugar), no soda of any type, and increased fruits and vegetables, may improve him, before Doctor-2.
Good Luck