You consider that "the full story?" I would consider this article as Mr. Baer's side of the story with an obvious slant by the author against the school board.
It is apparent that Mr. Baer will contest the Disorderly Conduct charge, as is his right. Maybe the city attorney or the judge will toss the charge to make it go away, however, just based on the video linked in the OP, Mr. Baer was given the opportunity to speak, he exceeded the time everyone was allotted, he was asked to leave and chose to stay, his actions disrupted the public meeting, therefore IMO, Mr. Baer is guilty of charge of Disorderly Conduct. If he knowingly chose to violate the law in order to bring attention to this issue, it is a clear case of civil disobedience, which I have no problem with.
When people disagree with a law and they knowingly break the law to point out the injustice of the law, that is free speech.
I'm not defending the book in question or it's use in a 9th grade Honors English class. I am defending the police officer and the right of anyone who is conducting public business to do so in an orderly manner. There were other ways Mr. Baer could have addressed the issue. He acted how he acted and the fine, if he is convicted of the charge, is $1200. Based on current advertising rates I would say that is cheap publicity for the issue he chose to raise with the school board. I would assume there are people who are already donating to help defray his out of pocket expenses.