Jamie,
My 13 yo son is on 54mg Concerta. He started on 18mg in early August (first time on meds), and he felt no different, so the doc upped to 36mg, and he still said he felt no different. He is not hyper, just inattentive, so it was hard to tell in the summer if it was making a difference. The doc upped it to 54mg, and he still says he is feeling no difference, although I do think he is being much less forgetful and more focused when doing homework. I now wonder if we could have stayed on 36mg (or even 18mg) with the same results.
He has had no side effects at all from Concerta so far, is able to eat and sleep fine. He is a very tall and skinny kid (5'11", 130lbs), but weight has nothing to do with the dosage. I'm in the opposite situation as you, wondering if I should ask for a decrease and see how that works. If he was having adverse side effects I definitely would do that.
Good luck to you,
Neelie