there was a picture of a gun on the t-shirt, that is what the school is most likely going to argue, and i will keep you guys updates on everything, this started last year...so it may to a while to end
He'll lose. It's somewhat along the lines of bringing a gun to school, not intending and not shooting anyone with it, then suing the school for taking it away and expelling them.
Also, I don't know if this is complete bullshit or not (sounds like it) but my English teacher said that any Government Association or something has to give you their approval to sue them.
lose.. he cant wear clothing that goes against the dress code in the school, especially if it is going against any value/religion/beliefs of the other students