I have AS, and though I'm much older than your son, I also tend to hide it during school and act almost normal, but then the behaviour all comes rushing back at home, even exaggerated as you can't suppress who you are forever (sorry for the cliche), as I'm confident my parents will understand why I'm acting this way. This is all subconcious of course, so although your son may not be able to put it into words, he may be the same.
Hope I helped