Where I work there are several lovely children with ADHD and a couple who aren't quite as lovely. For some of the children ritalin makes a huge difference. It makes it possible for them to attend school and concentrate to get basic skills.
These children aren't naughty and there is something completely and utterly different about them. Some of them sit or walk awkwardly or they struggle to make eye contact or their language is slightly stilted.
Prehaps ADHD is over diagnosed, but it is still a real condition. I am truely in awe of parents who have children with ADHD. The people who say they are bad parents should offer to babysit.
ADHD is an area that requires more research.