You could be right about wealth, though I'd be surprised - it would be really weird if wealth effects in the US caused Asian Americans to perform almost exactly as well in school as Asians, and white Americans to perform almost exactly as well as white Europeans.

But this doesn't change my original point - US schools do only slightly worse than Singaporean schools at educating people with an Asian-style home environment, Asian genes, or whatever else being Asian is a proxy for. And cultural factors in black America may cause black Americans to perform worse than whites and African immigrants. Whatever the underlying factor is, it has nothing to do with the school system. That's the only point I'm trying to make.