My Mother said I did the same thing when I was little. It sounds like you have an intelligent child who gets bored easily. This may be a precurser to a chemical imbalance in the brain. Monitor the child carefully, and see if there are any other signs of discomfort. Many psychiatric disorders, very treatable ones, manifest in the early to late teens. Does he respond to stimuli as other children do? Does he have a low frustration tolerance, is he combative and uncooperatove, these are things to keep a 'heads up' for. Keep in close communication with school cousellors for information, so you are prepared if he diagnoses with Adhd or later on with a chemical imbalance. I have a mental illness, my mom suspected it, my Dad was in denial, still is. When I go for meds or therapy I notice the rocking and sometimes head banging in other clients waiting to be seen. 
