Although I don't think their punishment is appropriate (if this is truly a first offense) his actions were a little douchey ... as to first amendment, if he posted while on campus he doesn't have any rights (if he was underage when he did it) ... if he was an adult, instead of a minor, or he did it off campus he might have that defense, but only if he could prove that his posting didn't actually violate a school policy
The courts have usually given schools a fair amount of leeway on constitutional rights ... the first, fourth, and fifth rarely apply on school grounds and minors aren't usually afforded the full protections of those amendments until they become adults (age of 18)
Bullshit. Those rights are only curtailed as necessary to make the school function. Its actually supposed to give the schools a little lee-way but its being abused horribly. Children DO NOT check their Constitutional rights at the school door.