When McMillen decided to fight the district's decision, she gained nationwide attention and support, including a scholarship. I suspect the glare of publicity was even more unwelcome to the district and its supporters than the eventual court ruling. Bullies and abusers thrive on silence and darkness -- they like their victims quiet and isolated from potential help. Sunlight, as the saying goes, is the best disinfectant -- open discussion of what's going on forces the bully to defend behavior which is quickly revealed as indefensible. The district retreated to a claim that the cancellation of the prom actually had nothing to do with McMillen -- something plausible to nobody, and quickly brushed aside by the court. The public humiliation will probably serve as a better deterrent to other bigots than the ruling itself.
The case has a whiff of Rosa Parks about it. Bigotry makes itself seem normative partly by arbitrarily denying its targets the right to do perfectly ordinary, trivial things (sitting in a certain part of a bus, taking one's girlfriend to a prom), and so when one of those targets insists on doing that ordinary, trivial thing, which would pass unnoticed if done by anyone not a target of the prejudice, the forces of bigotry have to blow it up into a huge conflict -- which reveals how stupid and nonsensical their arbitrary exclusions really are.
A point of interest from the ACLU report is the Mississippi Safe Schools Coalition, a statewide youth-led group which has been supporting McMillen and is sponsoring its own party in May as an alternative to discriminatory official events (not surprisingly, this is a common problem in Mississippi); its mission is "to educate teachers, students, and administrators about the rights of LGBT students with the aim of making schools safer for all." That young people are organizing like this, in a state as conservative as Missis-sippi, is inspiring. The future really will be different from the past.