pascha bchochma- There are many theories of what the cause of ADHD is. In the US mental illness is defined by the DSM, not by anonymous bloggers. In the last edition of the DSM, ADHD is classified as a Mental Illness. It will also be classified as such in the next edition, but they might change some terminology.
PB writes- “However, medication is not necessary”
Please see my post above how to treat it. Medication can very well become necessary if the behavioral therapy can’t control the child.