“Poverty” might be the cause, but it’s not just poverty by itself, in the sense of how every country has a spectrum of rich people and poor people.

Look at NAEP scores: https://fordhaminstitute.org/national/commentary/some-racial... (Table 1). Asians average 312 in 8th grade math, compared to 293 for whites and 269 for Hispanics. The gap between asians and whites is almost the same size as the gap between whites and hispanics. But the poverty metrics for asians and whites is the same: 8% below the federal poverty line. (While asians are richer than whites on average, the subset of both groups who have kids is more similar. There’s a lot of high poverty asian families in places like NYC.)

Why is there such a big gap in test scores between whites and asians when economically the two groups are similar? There must be some additional sociological factor at play behind poverty in and of itself. One might hypothesize that selective immigration plays a role. The majority of the U.S. asian population is foreign born, and is in the U.S. as a result of skilled immigration. That might have an effect on their kids test scores that’s not accounted for by household income alone. That’s the kind of additional sociological factor that countries like Japan and Korea don’t have.