Your posts sounds too familiar :S....
Try a quiet corner with headphones that block out all sound (or even plays music...classical)
I made my teen wear these recently and he was able focus on his work better and I placed his desk in a corner where there would be no distractions. Now that he is able to describe and communicate what keeps him from completing his assignments, he says the earphones help him tremendously. Sometimes, I have to remind him it's time for bed because he had no idea how much time has passed. I wish I thought of this earlier when he was in elementary school.
Anyway, I think the classroom just naturally has too many things to take away his concentration. He was minimally engaged in his assignments and knew what everyone else was doing as well as where the missing pencil is.
