Can a school suspend a student if they posted about the school on facebook?

[Michael]

Today our school's fire alarm sounded and was evacuated and the fire department responded, during this time i posted on facebook "the school's on fire". Later that day i was suspended because a parent saw the post and called the school, far after this they found that a sensor had failed. Most of the other calls received were because the fire trucks were outside the school with their lights and sirens on. I just want to know if it was legal for the school to do that, i was also forced to log into my facebook at school and delete the post and write that it was a false alarm, is any of this legal???