That was in specific response to the claim by grapeape that a cop can enter any public space whenever and wherever he wants. I believe you would disagree with that sentiment.
Is your argument only that he did it during off hours.
Actually, he did it while he was on-duty - and he was outside his jurisdiction at the time. There are other ways to accomplish this - parents of the students in question should demand to see the classroom and petition the school board. If the school board is unresponsive, since the article states that the community is conservative by nature, it should be easy to replace them. That is the way this is done, not by a rogue cop abusing his powers while on the taxpayer dime in pursuit of his own agenda.