It's difficult to draw meaningful conclusions from country-level differences like this, especially when the countries are as dissimilar as the U.S. (pop. 340M) and Singapore (pop. 4M).

Looking specifically at PISA, it's not usually administered at the state level in the US, but when it has, individual states have outperformed national scores, as one should expect.

For example, Massachusetts has scored similarly to Singapore in Reading and Science (zero or small statistical difference between) and not far in Math.[1] It would be a reasonable hypothesis that a PISA score for the Greater Boston schools (pop. 5M) would even further outperform the U.S.

Sweeping country comparisons tend to amplify noise rather than reveal a clear signal, and are often about regression to the mean as much as anything else. It's not impossible to make sound inferences, but it's difficult to avoid motivated reasoning.

1. https://www.doe.mass.edu/news/news.aspx?id=24050

It’s not clear to me PISA scores mean anything, because they’re not uniformly administered in the U.S. And if the scores are reliable, they point to distributional issues outside the educational system. For example, Asians in the U.S. perform comparably to Singaporeans: https://www.edwardconard.com/macro-roundup/us-asians-scored-.... White Americans perform comparably to Japan and South Korea, and ahead of all of Europe.

Since there’s no test which currently compares the best American 15-yos with the best other OECD 15-yos, we can’t assume anything about potential results. The best we can do is look at the data which exists and learn from that.

In general, I’d caution that presumptuous ideas like “best Americans will always be best” create cultural rot, and then something like DeepSeek happens. The cultural rot deepens when the elites run around trying to save face instead of admitting an opponent’s ingenuity, and aiming to do better. But I am not sure if that’s what you’re trying to imply (that best American students will out compete best students from other countries) but that’s the sense I got from your comment. America is resting on a lot of built-up wealth and power, so even objectively mediocre elites do well here.

I think everyone already knows this, but success in American society is predicated on intergenerational wealth and/or charisma, which is how people like George W. Bush or Trump become presidents despite being academically mediocre. People who make promises of meritocracy would never appoint some natural genius person-of-color as Barron Trump’s boss, for example. How likely do you think that is?

I’m not saying anything about the “best American students.” But America has unique social challenges—former slave society, mass immigration—that European countries and Singapore don’t have. Those impact test scores, but that doesn’t mean there’s problems can be fixed by schooling.

P.S. “person of color” isn’t a category that exists.

Education is the purview of the States, not the Federal Gov. So if you're comparing scores you have to compare Singapore against individual States. You will find a HUGE disparity between states. Some do quite well, close to SG levels. Others are abysmal.