If teachers weren't doing anything questionable in class, why would they care if parents were notified? Shouldn't teachers be relieved that parents be notified because it may increase parent - teacher involvement and relationship.
On the other hand, if a teacher was doing something questionable, then they would have a strong reaction, like what has been happening.
It's just like a girlfiend who suspects her boyfriend of cheating and she asks to look at his text messages, if he promptly hands the phone over, no problem. If he says, "just a minute, then runs to the batthroom and furiously deletes texts and acts upset that he's even being questioned at all. Then guess what?
