The shooting "victim" was a bully and a predator. The shooter was a victim of that predator and could find no help from the school. This is a sad situation, and I would not enjoy serving on the jury. The shooter committed a crime, but he was set up by the society that should have protected all the children in the school and not just one freak who enjoyed being a bully.
An intelligent teacher might have told the bully that, yes, he had according to the school a right to act like a freak but that he would have few friends in school and miss out on the chance to learn how to make friends if he continued abusing others for the fun of making them squirm. An intelligent administration, confronted with an unacceptable lawsuit risk on one side and an unacceptable risk to the normal children on the other side, would have "allowed" the little bully to dress as he liked but provided continuous supervision to keep him from using his freakishness as a source of power. There were so many opportunities to do this right (including standing up to the parents and explaining that even if there was a legal right to dress like a freak, it was harming their child socially), but the school and the family did nothing.
I suppose that sounds good in theory, but it is neither reasonable nor possible to provide "continuous supervision" of a child who is determined to harass others, especially when that child is obviously not responding to normal motivational techniques. The simple reality is that the kid was on a collision course with what most of us rightly define as normality. The only way to stop that was to take him off the course, as his English teacher tried in vain to do. Meanwhile, the teachers who got praised were the ones BUYING him dresses, evidently beloved of administrators who thought of that (and bathroom squirming, I guess) as constitutionally protected.