I think this can be misleading in the same way some charter school results are. The easiest way to improve a school's results isn't to improve the education provided, it's to get rid of the worst performing kids. Charter schools do this by various selection effects, and artificial barriers, like ending at noon on a Wednesday. So the only kids who go there have two parents, one who probably is stay at home and can pic…
Education is mostly about your peers. It's obviously true for prestigious universities but it's just as true for elementary schools. Charter schools kicking out problematic students isn't some loophole, it's the main point, and it absolutely can improve the education for those that remain. My district has a quarter of high schoolers in charter schools. Almost all of them under the poverty line. It's not like they're…
It's the main point for people who want their children to succeed at the expense of the rest of society and it's a loophole when they try to sell that concept to the rest of society as "we can teach better for cheaper so give us your tax money and let us replace universal public education" rather than "we have thrown some of your children on the scrapheap for you to expensively support for the rest of their lives and either don't understand or don't care that this is of net negative value".