I agree that, although 6 year olds can be tempermental and know it all, you seem to be dealing with some very unusual and unpleasant behavior. Autism comes to mind. Anyway, this sure sounds like a whole lot more severe than a simple case of ADHD. Why don't your try posting this on a couple of other forums here as well as this and see what responses you get. What does the specialist say he suspects?
Best of luck. You sound like you're really on the right path to get the answers that you so desperately need.
It also sounds like he has some sensory integration issues-- the physical things like the tags on clothes, shoes bothering him as well as the visual things.
And yes, unfortunately 5 year olds are that mean. So are 4 year olds. My son had toileting issues in pre-k and was teased A LOT even though the teachers intervened whenever they caught it.
It sounds like you're heading in the right direction with the behavior/development specialist.
Perhaps it would have been a good idea as the child was put in day care at a very young age and had problems fronm the begining including I suspect ,Seperation anxiety to have checked out the day care ,to see if the children there were looked after, had enough attention , and stimulated, not bored ,that will make children act out. Reading your post it does sound as if because he has spent so much time with other care givers the problem has stemmed from this, however he needs help now ,perhaps a good idea for counseling for the Famil;y