This is not the doctor link, but as a parent and former teacher I can give you some suggestions.
My son has behavior problems when he eats foods with red dye and or sugar.
His behavior has improved since we started giving him protein based meals. Also we started giving him children's gummy bear vitamins without the red dye. A child this age needs to have about 12 hours of sleep. Is your son getting enough sleep at night?
my son is the same way. i am at my wits end of how to help him at school. his teacher sends him to the office everyday and they have isolated him from his kinder class all day and all week. his first day back to class he acted up and was sent back to the office. what do i do? he also is very smart and i think he is must be bored with kindergarten. i also feel at this point a different teacher would be the best for him, he is isolated everyday.