There is some interesting literature out there about IQ gaps in minorities and in particular in oppressed minorities.
For instance, in Japan, Burakumin (a caste-like minority) and Koreans (an oppressed minority in Japan) have very low IQ scores and poor school performance relative to Japanese. The Burakumin have a 15 pt gap in IQ. However, it is said that when Burakumin immigrate to the US, in the second generation, the 15 pt difference evaporates and their children score even a bit higher than Japanese.
Japanese Koreans are also said to do very well in school and on IQ tests in the second generation after migration to the US, but they do poorly when they are in Japan.
There are also other examples of IQ score differences between close neighbors in the same nation who would appear to have similar genetics, for example between French vs. Flemish speakers in Belgium, Irish and Scottish vs. English in Great Britain, and Afrikaans speaking Whites vs. English speaking Whites in South Africa.
Children of immigrants of all types seem to score higher than those who stay behind. This difference is mysterious and apparently cannot be accounted for on the basis of selective immigration. Something about immigration itself seems to stimulate cognition in immigrants and their children.
- Sternberg, Robert J. (Editor), Grigorenko, Elena L. (Editor). 2001. Environmental Effects on Cognitive Abilities. Hillsdale, NJ: Lawrence Erlbaum Associates.