Attendance is one bit of information (present/absent). Perhaps you can add exact time of entering and leaving which would make it a couple of dozen bits. There

Attendance is one bit of information (present/absent). Perhaps you can add exact time of entering and leaving which would make it a couple of dozen bits. There is no need to record more information than this. The expectation of privacy is exactly this: that any information that is not needed is not recorded. Human teachers are unable to capture or keep recorded all the extra information they see with their eyes. Cameras do.