Our elementary school has many wiggle seats in every class, especially among the younger kids. (such as
http://www.amazon.ca/Wiggle-Inflatable-Sensory-Chair-Cushion/dp/B00JCJ9IYE)
A good teacher will also allow kids who need it to work standing up, which can be a huge help (and for which there is growing evidence, for adults too). I'd echo GGG and ask the principal specifically to match your child with a teacher who is comfortable with a moving body in their class. It's no disruption at all with a teacher who doesn't themselves have a problem with it, but can be miserable for a kid if the teacher misunderstands it as a discipline issue.
