A NY Times article says:
Many education experts say that until teacher quality improves in urban schools, student performance is likely to stagnate and the achievement gap between white and minority students will never be closed.
This is another example of the bad policy decisions that are made when human biodiversity is ignored. If the "achivement gap" between whites and "minorities" is genetic in origin, then endless attempts to improve "teacher quality" is just a big waste of resources.
Because there are millions of school teachers, and it's not the world's highest paying job, it's impossible for more than a small minority of them to be more than just average.
The article also contains some interesting stuff about a plan to evaluate teachers based on how much their students improve their performance on standardized tests. This, to me, sounds like a reasonable basis for evaluation. The teachers are opposed to it, and I understand why. The more scientifically you are evaluated by management, the more prole-like your job becomes. Teachers don't want to drop in class.