Charter schools deliver results the same way that private schools deliver results: selection bias.

It's really easy to have good outcomes when you have the ability to curate your student population. And though charter schools are regulated to make it harder for them to curate their student population, the statistical evidence is pretty unequivocal: they serve different populations than public schools, and their "better outcomes" immediately vanish when you control for that.

So, what is the issue with redirecting funding from sucky* schools towards ones that deliver results**?

* Schools that teach the general population

** Schools that teach a subset of the general population that always does better

One obstacle is geography, and the built environment. Schools are of their communities. Even if you do bus people around, they come home to the same places, norms, and situations; not all education happens in the classroom, and “you don’t belong here” is a thing. The rich schools are in the rich places. The poor schools are in the poor places. The outcomes—often—not always, but often—reflect that. Is a deeply-depressed neighborhood really improved by starving its school? Or deeming it unworthy of a having a school altogether, and emptying its children out to places that “have it more together”?

Another is the idea that schools are motivated by money in the same way profit-seeking ventures are. A company’s shareholders might respond to financial threats and incentives, but the teachers on district-regulated wages? What’s the phrase, can’t squeeze blood from a turnip?

Then there’s of course the construct validity of standardized tests as a measure of “suckiness”—they’re easy to administer at scale and to compare across years and between schools—but do they really capture every flavor of good work that’s done at a school? They’re the best thing we have, but does that make them good enough?

The main issue, though, I think we can frame in terms of a slightly different legibility issue: since the school is the only variable we directly control, we model the school’s “suckiness” as a function of its… what, budget? Staff bonuses? Whoever exactly is it who we’re proposing to punish by removing funds? But just as I imagine we can think of kids who would be fine either way—one of the less provocative stereotypes that comes to mind is that of a Tiger Mom kind of community—we can probably think of kids who won’t be fine. The less provocative stereotype that comes to mind is a child with special needs: with an aide, maybe that child may develop enough to participate in society, and we’re a more humane and moral society for trying. For that matter there are other children who are living and growing up in situations where survival is always going to come before their test scores—and those are probably the students with guardians least equipped to exercise “school choice.” How does punishing their school improve those kids’ outcomes?

Often students who perform poorly need more resources, not fewer.

…are a few of the counterarguments, anyway.

Because it’s not a real choice. As household income decreases, the odds the child goes to the nearest school (regardless of how good it is) increases.

Are you providing after school child care options or transportation to their school of choice? If not, then it’s not a real choice and kids from lower income households will remain disadvantaged.

That is to say, the results will be mostly identical except now public money will be going to private entities. Because that was always the real goal of charter schools.

Because the "sucky" schools are statistically where poor people go to school, which statistically is where minorities go to school.

School choice is bad because the only people who benefit from school choice are already wealthy - they can afford to transport their child to the school of their choice.