>Given how little the US invests in public education, probably never

While I understand the sentiment, this isn't factually true: from figures I've seen, the US actually spends more per student in pre-college schooling than any other nation.

It's a lot like the US healthcare system: the US spends (much) more per-capita, but gets much worse results overall. The problem isn't the level of funding, but how it's used and who runs it.

Another factor is US education is that the funding is largely from local sources and locally controlled, so if you live in a wealthy county, you might have (relatively) very good schools, while kids in poor counties will have poorly-funded schools. This is mostly a problem unique to the US because it loves keeping power at local levels so much.