Comment by brightball

From the teacher's I've talked to, it's teacher work conditions related to student behavior that are creating more problems than anything else.

Disruptive students in particular who negatively impact everyone around them but for whatever reason, are frequently not removed from the environment. It's also driving a lot of good teachers into retirement.

When you see clusters of poor performance, my guess is that it's associated with regional policy creating a poor environment rather than a total absence of quality teachers.