Volokh quotes a review by Clarence Page that contains this nugget:
Among the most intriguing possible reasons for this disparity is an intriguing group difference in the way students measure their family's "trouble threshold," according to one study that the Thernstroms cite. The "trouble threshold" is the lowest grade that students think they can receive before their parents go volcanic with anger and start clamping down on TV time, etc. In the survey by Laurence Steinberg, a Temple University social scientist, published in his 1996 book, "Beyond the Classroom," most of the black and Hispanic students surveyed said they could avoid trouble at home as long as their grades stayed above C-minus.In critique of this, my wife (whose background is in education) points out that Asians have a particularly high suicide rate perhaps derived from such standards! My counter is that too much ignorance leads to an unacceptably high homocide rate.
Most of the whites, by contrast, said their parents would give them a hard time if their children came home with anything less than a B-minus.
By contrast, most of the Asian students, whether immigrant or native-born, said that their parents would be upset if they brought home anything less than an A-minus. [Emphasis from Volokh.]
In the end, the world is not a simple place and lots of factors matter -- not least of which include nutrition and genetics. But I believe that downplaying the role of culture is wrong-headed in the extreme...