There are still problems with teacher who have tenure sometimes. It's not that they can't be fired; generally it's that the administration doesn't want to do all the paperwork necessary.
Yeah, I worked in California, had ten years seniority. In CA you must join the union, (you do get the big liability policy). The firing of teachers is impossible, because where I taught the teachers owned the board. In one school, good administrators were released four years in the ten I was there. Reason? They did not get along with the teachers, (thought teachers should pull yard duty..Etc.) which the teachers considered beneath them. I was one of the youngest teachers (at age 26). I was quite liberal then, but I still believed in teachers really knowing the subject and working hard, so lots of teachers were not sad to see me go.
We had a retraining program, where we were taught to relate teaching skills to the "real" world. (We did not teach, we planned and managed a large group of people and conducted evaluations of their acheivement.) When I went back to Engineering at Lockheed I received a 20% raise and was able finally to start saving for retirement. (I still loved the teaching part of the job and arranged to do teaching of engineers part of the time in aerospace.)