as andy pointed out, some people here are forgetting that this kid does not have a legal right the wear what he wants so long as he is a minor. he must live by the rules that his parents set for him. so his parents are ok with it you say? he must also live by the rules that society sets. in this case the no visible piercing thing. he must learn disipline.
study psychology and you will see that he does infact have issue to deal with. as do we all. the difference here is how we deal.
to the person who compared this kid to dr. martin luther king jr: wth? are you really serious? dr king promoted peaceful demonstrations within the boundaries of the law, not abandoning the law, or rules, whenever it suits you. more importantly, the civil rights movement was to get equal rights and treatment for people who just happen to be a little darker than the white people. not because they made a choice to be black as this kid made a choice to wear the visible piercings.
here is a good opportunity for this kid to do something productive. start a petition by getting the students to sign saying they think the rule should be changed. get the parents involved. have the rules changed be going through the system as opposed to flipping the bird to the system.