Your statement is uninformed. ADHD is real.
I agree that ADHD is overdiagnosed, but ADHD is a real pathological condition with a biological substrate. It is a matter of ongoing research by neurologists. Those who have ADHD are not just "kids being kids".
I had a severe case of ADHD as a child, back in the 1970's when the name for the condition was "Hyperactivity". I knew perfectly well that I would keep getting in trouble and be rejected by my peers if I engaged in behaviors such as singing songs in class at inappropriate times, but I could not help it. No amount of punishment from my teachers or parents made the slightest difference. I would continually resolve to stop misbehaving and to start paying attention in class, and I certainly punished myself enough for being a bad kid, but I see now that no amount of willpower could change the basic biological problem.
When I finally got a correct diagnosis and started meds (which, in those days, was Dexedrine), the problematic behaviors stopped as abruptly as if a switch had been flipped. My grades immediately went from all F's to all A's. My teachers, who did not know that I had started meds, were astonished at the sudden change.
Fortunately, I largely outgrew the condition in early adulthood. That is not uncommon in cases of childhood ADHD.