Not being disciplined for speaking your mind doesn't mean they don't have the potential to. You already have limited rights as a minor, you surrender even more on a school campus.
When I was in school, we had a full-time deputy on campus. Police weren't "called" but he was active in normal campus discipline, writing tickets for petty offenses like loitering and truancy and possession of cigarettes, etc.
/had to go to court once for ditching