If it was a private school then yes, they can kick out pretty much anyone they want, for any reason. I'm sorry for what happened...maybe you can request an arbitration to get your son back into school?
proof...
I can prove that my clothing was on the show, of course. Also, the dancers will testify(?) that the clothes were made by me.
Nobody is given the costume credits on that show. I also have several saved emails addressed to him asking about the missing credits.
As for damages, that...
I was paid $200 several months ago to design and sew 2 costumes for a local TV karaoke show. Part of the verbal agreement was that I would be listed in the television credits, which did not happen. The producer has been ignoring my emails asking why and in fact has told me to not contact him...
Several months ago I designed and sewed costumes for a late-night television karaoke program. As well as paying me for them, the producer promised to include me in the credits as costume designer for all the shows. Of course, he didn't even put me in one! This was a verbal agreement...