My son just turned 8 when his little sister was born. they are now respectively, 11 and 3. Johnny is an exceptionally bright and rambunctious child, scoring in the 97-99th percentile on the standardized tests but always mediocre grades when behavior was factored into the equation. Grades 1-3 were the toughest, and he actually improved dramatically over the last 2.5 years. He's in 6th grade now, and while not perfect, he has outgrown a lot of his issues in the classroom.
If the doctor and you do not believe he has a medical reason for his extra energy, I am inclined to believe YOU, not the teachers. They are often overworked and have a heavy load of children with real academic difficulties, and many of them do not have the resources to deal with a child who is most liekly smarter than the rest. He is probably siginificantly bored in the classroom AND craving attention. I would definitely NOT medicate my son!
Johnny improved significantly with a combination of things. One was getting him into a classroom, which happened in 4th grade, where he had a good teacher. She helped steer him towards more productive activities and helped him find outlets for his drive. His little sister actually helped in a lot of ways too-we increased his levels of responsibility at home. We signed him up for scouting.
We were still feeling frustrated though because the school wasn't meeting his needs. We looked at private schools (ouch) and also considered montessori--which becomes much harder to apply at 6th grade, so if you go that direction do it now! But you have to get your son out of that negative environment--it is really detrimental for your son to be heariong that kind of response over and over from his teachers.
We moved out here in August and spent a LOT of time looking and comparing public schools in the different towns before we decided where to live. Real estate is expensive, but private school is more so! We are realllllly happy with Johnny's new school and he is improving dramatically. He still has to be called upon to stay on task once in a while, but he is doing a lot better with teachers who give him outlets for his academic growth while still helping him to focus upon his weaknesses--organization and focus. Not an adhd case, just a very bright child with an active imagination, which I am guessing is your son as well.