The funding thing's a red herring. The best-funded schools in my state, with by far the highest spending per pupil, excluding special cases (e.g. schools that are also correctional institutions or otherwise not an ordinary school, so obviously have sky-high costs), are also among the very worst we've got, and it's looked like that for years. Throwing more money at schools in poor areas has had little effect on outcomes—not to say we shouldn't even out funding or even give poor-performing schools extra funding (which we already are doing, and if we just evened out funding, we'd be taking money away from the schools in very-poor areas and giving it to "richer" ones) but it very much does not look like doing that will have much effect on educational outcomes.

Money is part of the cause, but where it comes in is letting parents sort their families into expensive-to-live-in school districts with other parents who could also afford those expensive areas. Their kids tend to be easier to teach for a whole bunch of reasons—which does make the schools more effective, but is not because of extra money spent on the schools. The sorting enabled by money does matter, but the funding itself (received by the schools) does not appear to be a major factor.

Basically, a family pays for school quality in the US no matter what, either directly or indirectly—you pay either with tuition for expensive, good private schools if you're fairly rich, or with real estate and transportation costs if you're not that rich, with a sliding scale all the way down to "practically destitute". The extravagant spending of expensive private schools might result in better education (I'm thinking especially of the very-small class sizes, like 4-8 students per class, and the ability to pay for content-area PhDs as teachers in higher grades—we'd have to triple public school budgets to do that stuff, and that actually wouldn't even be enough because demand would so badly outstrip supply, should we try it) but beneath those relatively-few outliers with far-higher spending, moving spending/budgets up or down a (relatively) little doesn't seem to do much.