> The point here is that we have no idea how to make a school good, other than by kicking out bad students

I would disagree with any metric claiming to measure school quality that is not constant when the demographics of the school change. If our metrics simply gauge the socioeconomic status of a school's population, we need better metrics. We also need to develop interventions that overcome the educational costs of poverty, perhaps, dare I say, by eliminating--or at least attenuating--poverty.