Teacher's Unions are not the sole problem. I do agree that the majority of teacher unions are little to no help in today's society. If you compare the salaries of a union teacher vs a non-union teacher (private schools) they can vary widely. Particularly among smaller suburban catholic schools. Its been scientifically shown that expectations create who you are (citation needed). If your teacher constantly says your dumb, I wouldn't expect you to get it right, etc, the student will will become that person. If the teacher says 'your going to do great one day, keep up the good work' that student is going to become great. Now yes thats not 100% true, but expectations from your teacher is a huge influence on a student's performance. This thinking can also be applied racially.... but thats for another time.
There will always be victims of circumstance, and teachers that are better than others. I think we need to improve the education for teachers, and perhaps have some sort of personality assessment. FTFA teachers that expect a lot from the students, get a lot from the students. So rather than saying FIRE THE TEACHERS! maybe we can do some retraining. Just some thoughts. Here's a penny.