I posted the following suggestion as a comment to this WSJ article
A significant part of the teacher competency problem is no fault of the teachers. It starts with the training they get in college. Many high school teachers are especially penalized by inadequate preparation in their subject. This is no fault of their own. I have taught many prospective high school teachers. They are generally committed, smart, and willing to work hard. But many universities, concerned more with marketing and “happy consumer” goals have moved the pointer all the way from grade inflation to “content deflation”. That is why I recommend that universities be required to take teacher competency tests. How? Require that teachers take competency tests and make the results anonymous except for the college they attended. Then publish those statistics.
I have never quite understood why, when teachers appear to lack expertise, no one questions the institutions that trained them. What company would keep hiring welders, for example, from a technical school when those welders didn’t know anything about welding? Of course, the welding school would say, “It’s the students. I tell them to learn. They just won’t do it. So, I give them A’s and degrees anyway.”, or, “Oh, they learned from me. They just keep forgetting! “