“If this is a public school then it is a government agency.”
It is not a public school.
Having been monitoring this thread, I’ve noticed that quite a few folks seem to start with the assumption that this is about what a public school can/can’t do. That would make the girl (in the eyes of most) the hero in this story. But, given that this is about a private school, about individuals making a conscious choice to attend such a place, about the rights of private individuals/private businesses to establish their own criteria for standards of behavior, etc., then the girl becomes the one who is in the wrong. I do have a problem with the excessive nature of the fine and, if it is not one that is stipulated ahead of time, it tends to make the institution sound petty.
As for those whose libertarian sensibilities have been violated by the school’s tamping down on this student’s “rights” to express herself, get a grip. Young people are to be instructed in the ways of the world. Decorum is one aspect of those ways, always has been. Maybe, because we see so little of it anymore, it is beyond our ability to recognize its necessary place in society every now and again.
How do you know that? It is not in the article. If it is a "Charter School" then it is a quasi-govermental agency and must adhere to the constitution as if it were a government agency.