It depends on his age. Yes, the school has the right to suspend
him - it is school polity. HOWEVER, I think it would be
beneficial to bring him back in and use it to discuss civil
liberties in social studies classes and use it as a way to teach
civil disobedience. I'm sure it will be used as an example case
in other high schools and colleges if the story goes nationwide.
The danger of course: Will this encourage further civil
disobedience and is the school prepared for it? Is it possible
to put the genie back in the bottle? "