How old is your son? My son is 5, and he uses body movements as well to express his excitement. When he was 2 and had just started walking, when I would take him to the pool, he would just walk in circles around the pool. If we went to the park, he would just take off and go and not really show too much interest in the playground equipment. I think some of this is normal childhood behavior too. My son has settled down some. Now he will stay with me in a store and not run off down the aisles. He does still like to run though when we are outside. Sometimes he will jog in place too if he is excited.
As far as school, has your son been officially diagnosed? If so, what type of school is he going to? If the teachers are trained and knowledgeable in the area of autism, they will more than likely be very used to this type of behavior. That is part of the learning process too, for the child to start learning that there is a time to sit still and a time to run. As your son is still young, I would not worry about it, and just let him get his energy out!