There are two separate issues being discussed here, and the confusion of the two complicates the clarity.
There is considerable empirical support for psychiatric illness, and there is much discussed even in the Talmud. While psychiatry is a soft science (as opposed to hard science – those about things that can be accurately observed and measured), it remains a science which is primarily based on research, not theory. Whether something is a legitimate illness or condition is something i would seek from research, not commenters in the CR. Anyone is free to have an opinion, but one’s belief does not constitute fact.
The second issue is the child in the school setting that is not performing according to some preconceived notions. This calls into play the mission of the yeshiva/classroom, what is the understanding of a child’s inability to perform to perfection (or close) on academic tasks (such as tests), and the ability of the school and faculty to accommodate to help the child.
On the latter, the ADHD diagnosis is a legitimate one, though it has its naysayers. It exists on a spectrum of severity, and there are a variety of symptoms that can exist in various combinations and levels. It is a problem that there are those that fling this label wherever they want, while lacking training to know just when to apply it. It is abused by many in the education field, sometimes being ignored, other times being used to label a child unnecessarily. I bet the medications are overused, but there are also times when withholding the medications is a mistake. The ideal would be for experts to make these determinations. It is often that the symptoms of the ADHD issues are observed in the academic setting, and hardly elsewhere. This responsibility falls on the educators, many of whom are not equipped to handle it.
Just as one cannot use discipline to treat a fever, it is misapplied when used for learning issues, ADHD, and many other behavioral problems. There is a role for discipline, but it often requires much to know just when it is appropriate.
We need not to confuse the issues of mental health and education.