The problem is so many children have been misdiagnosed by a flawed and corrupt system. I'm not denying the existence of add or adhd. But i have seen myself how the school system has compelled the parents, and then together compelled the doctors, to get a diagnosis that is more in line with the wishes of the school than the reality of the child. The kid misbehaves, maybe because of their temperament, maybe because of outstanding psychiatric reasons. The school wants him or her medicated, and if the doctor doesn't give them a diagnosis they wanted, the school threatens the parent to expel the child and quietly makes it aware that a different diagnosis would be within their capabilities to handle, and poof, a new diagnosis appears. I've seen it happen. And that and so many other very dubious cases of add and adhd from incompetent, corrupt, or manipulated doctors result in many feeling the entire disorder doesn't exist.
I don't agree, and I'm not saying the OP's kid isn't a completely legitimate case, but it's hard to blame them.