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.
Whatever the underlying factor is, it has nothing to do with the school system.
This cannot possibly be true. School system are artificial constructions created by men to serve men. They are not given laws of nature. The only thing we can tell from the above is that the current school system does not serve well black Americans. School system should adapt to whatever the "cultural factors" of the populace they serve.
Whether this should be through prolonging schooling hours; providing stronger and more persistent emphasis in personal hard work; correcting a harmful self-image; getting rid of institutional racism; using different instruction techniques; or any other method that may addressed the "underlying factor" can only be discovered through research, experimentation and a willingness to change and adapt.
It is easy to find examples of a schooling that adapts to the unique circumstances of some children, for example: intense language training for children from immigrant families, schools at hospitals or schools that follow a circus around the world (http://www.guardian.co.uk/education/2007/jan/26/schools.uk).
It may well be the case that one or both of US and Singaporean schools are worse at educating blacks/whites/hispanics than hypothetical school system you can dream up.
It is irrelevant when considering the question of whether Singaporean schools do a better job than US schools. For all we know, Singaporean schools might be worse than US schools - i.e., they could education Asians equally well, but blacks/whites/hispanics vastly worse [1]. But it wouldn't matter since Singapore doesn't have any blacks/whites/hispanics.
[1] You actually see this effect (Simpson's paradox) when comparing US states. Texas is better at educating blacks, whites and hispanics than Wisconsin, but appears worse when averaging over the entire population.
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.