Yes, SPDers can go from one extreme to the other. Sometimes it can be situational. Be hyper in one set of circumstances and hypo in another set of circumstances. That's what is so tricky about it.

This isn't the best example but i can't think at the moment: my older son can't stand to have his hands dirty. He fidgets and rubs them until he's able to wash them. But he is completely oblivious to any food or dirt on his face.

My younger son does very well at school, but as soon as he gets off the bus, he let's it all go. That's why I've been torn for a year now about having him evaluated and diagnosed. He has friends, he sits quietly, raises his hand, does well academically, but at home, he is a sensory seeker. It's because of his food issues that I finally made the call to have him evaluated (appt on the 13th--his 7th birthday). So yes, your son is probably doing everything he can to handle his day at school, then he feels safe at home to let it out.