re: selection bias, skimming the cream.. (charter v. private v. public)
Reminds me that in any/all classroom situations the most able students must be challenged and discover that they too can fail. An example of how important this is to character development is seen in some of the today’s personalities – W.J. Clinton comes to mind. This need not mean separate classes, nor brutal competition (save for hard-to-mature personalities like his). For some in this category requiring they successfully teach and tutor is sufficient.
Interesting observation about rural v. not schools. My sense is if communities of about 300,000 were sovereign in terms of most domestic affairs (over whatever area is required to establish that number) these things would sort themselves out, and there’d be enough diversity of opportunities in populous areas that citizens could afford to vote with their feet, as well as a ballot. There wouldn’t be one-best-answer, but lots of experimentation (and, the horror, competition). Texas almost has this with their ~1,000 independent school districts.
Granted, these were formed with less-than-the-best intentions (an attempt to sidestep desegregation), but they have kept the "self-government" muscles alive, at least in Texas. And created more than their share of able politicians.
Turns out a decade plus ago I founded a private school to meet some unique needs of prospective (international) employees. My sense is most all of what we value today is dust compared to what we leave behind in children that are happy, motivated and have been taught to love life-long-learning, irrespective of their abilities and eventual vocation. And there’s no one recipe to achieve this so parents must be free to choose, and teachers free to recommend an alternative (including going to work for a few years).