There is no such thing as student privacy.
At least not until they are 18 years old.
Before that, they are children to be guided by their parents first, and (with the parent’s approval and supervisión) by their teachers second.
But to many teachers, it is more like this:
“Before that, they are children to be guided by their teachers first, and (only with a teacher's explicit permission and absolute surveillance) by their parents second.”