THe story doesn't say (much of anything), but it could be that he wore this shirt on "homosexual" day at school (can't remember what it was really called). It was a day where everybody was supposed to be quied all day to show solidarity for homosexual rights. Many schools have teachers encouraging thier students to join, and I think theere are t-shirts and buttons.
If there are no t-shirts allowed with any pictures or words, I agree that none should be allowed.
Charles
Good point. As a protest it should be allowed. School ought to be neutral.