Free Speech vs Inappropriate Speech

Need some help. We seem to have an increase with the number of written assignments that are being turned in that, in one way or another, is bashing someone. Sometimes it's a classmate, sometimes it's a teacher and, believe it or not, sometimes it's the principal. When I talk to students about this, one of the first things they almost always bring up is the right of free speech. Now, where free speech is a right, at school, we draw the line in certain areas. Calling someone fat, ugly and stupid is just inappropriate, regardless of how you feel (besides....I'm not fat). Writing how terrible a staff member is, or that the principal should be fired (or as I like to call it, retire early), shouldn't be part of an assignment that they are turning in. Today at lunch I'm going to talk to the students, try to explain the difference and let them know it's inappropriate for school. It really falls under our Anti-Bullying program. Any help at home...as always...is greatly appreciated.