ADD is real, but horrendously overdiagnosed. It seems that in some places, all children are assumed to have it until proven otherwise (and we're also headed in that direction with autism IMNSHO). I can't find a link and the story sounds apocryphal, but I've read about schools which automatically referred all children who were not living with both biological parents, regardless of why, for ADHD testing. I don't get it either.
A good way to tell if the child really has it is if the parents (okay, mothers) brag about it. If they do, it's probably not the child, but the parent(s). Besides, it's NOT about violent behavior! Maybe a child who is killing pets, setting fires, acting out sexually, etc. has ADHD, but that is not why the child is acting that way.