Congress shall make no law respecting an establishment of religion, or the freedom of speech, or of the press, or the right of the people peaceably to assemble. When you are in school you cant say anything that will distract the learning of other people.
This might be a free speech zone but you can say something that might offend someone.
freedom of speech doesn't stop at school. Your right to say what ever you want when ever you want to say it.