Not just legit criticism of lesson plans. Parents are going to be complaining that their Johnny doesn't get more attention.

If it were a college, you'd have a point. But it's not college, where a lecture is given and students are expected to to do everything on their won. If a child is failing or doesn't understand the subject material, a teacher has a responsibility to get involved and help them out.

Parents are going to complain if their children get disciplined.

If they don't have a case against the teacher, no disciplinary action against the teacher would be taken. If they do have a case, then disciplinary action against the teacher is warranted.

It's not like children don't talk to their parents about what goes on in the classroom, whether they're telling the truth or not. Many kids have smart phones in class and also record what goes on, but only for stuff that they care about.

Also, it's not like teachers don't deal with bad parents as it is.

Worst case scenarios: cameras wouldn't change anything.

Best case scenario: cameras would tell us who's lying and who's telling the truth.

It's the same thing with cops wearing body cams and that's been one of the best things that's ever happened with law enforcement, for both the public and the police officers.