One of my son's preschool teachers told us that Dane couldn't be ADHD, since he could hyper-focus on things he enjoyed to the exclusion of everything else.
Duh, that is one of the hallmarks of ADHD! We went another 2 years without pursuing any sort of diagnosis because of that woman's "assessment."
Then kindergarten screeners recommended we hold him back...because he had no focus during the session (put a little car/truck-obsessed boy in a room full of his favorite toys and what do you expect, people?).
This is the same boy who now scores advanced on state standardized tests. Holding him back would have been a disaster. Instead of being just ADHD he would have been bored to tears and ADHD. Bucking their recommendation and enrolling him in an Montessori kindergarten (and subsequently a Montessori Elem. school) was the best thing we ever did for our kid. It was at that kindergarten that the school director recognized instantly that our kid was perfectly ready for kindergarten. She also worked with us and our son's pediatrician through the diagnosis process. Rather than writing him off as a "problem child," as previous educators had.