I have mover too. At 10 he still has trouble sitting for the amount of time his peers do, but it has gotten better. I agree with GGG's advice to talk to your principal. We have had great luck with our school in that DS is carefully assigned a teacher each year who will work with his style. The fact that he's a very bright kid who is very clearly still listening as he's walking around the room helps. On days when his energy level is unbearable, he is sent on errands to the office, the library, etc. or simply asked to go walk up and down the hall a few times to get the wiggles out. The fact that he is allowed to do things that the other kids are not (like get up and walk around the room) does not phase the other kids - they are pretty darn accepting.
I also agree with GGG that many many K kiddos can't sit still. In our school there are frequent movement breaks in the K and 1 school day (some teachers are better than others, but most embrace the need for it). In addition, they have a pretty high tolerance for kids who can't stay put.
Other things that have been tried with my DS and worked (albeit mostly for short periods of time - the best thing has simply been growing up...) include chewing gum during class, the theraband around the chair, weighted belt (at home, didn't take). If you truly are concerned and things don't go well right off, other things that are becoming more accepted are active seating, like the wiggle stools or ball seats where your body is always engaged and shifting to keep balance (not just a stability ball, probably something a little more stable than that for a 5 year old). I also have seen the bike pedals attached to a desk or chair - you can actually buy a relatively cheap version on amazon. If he truly can't not move, it might be a help if the school will allow it (I think mine would if DS really needed something more still...).
Good luck!
