I think observing is a good idea, but his behavior will change with you there. Maybe they have a window you can peek in? Or leave a video camera running? Or maybe just go and observe and ask the teacher afterward if that was a typical day.
With only 11 kids in the class, I kind of feel like the teacher should be able to help/problem solve to aid with keeping him a little more calm. It is not like he is in a class of 25. Maybe I have never stopped and thought about how much energy my son really has...he is my oldest, so I really don't have a comparision.
I would ask if it's really fair to him to be being kept calm at this age instead of following his natural inclinations? My very very calm, quiet five year old is absolutely bursting at the seams after a day at kindergarten because it's just so controlled. This is even with a morning and afternoon free play time.
