Hmmmm... immigrants often group together in immigrant communities where they are highly stressed and work extremely hard to assimilate and adapt to a new environment. This stress, hard work, and struggle for survival might have a huge impact on the kids who really push to succeed. Other kids in this immigrant community are swept up with it.
Remember the Hmong from Vietnam. Back home in Vietnam, they were not regarded as particularly bright... but once they moved to America, their kids performed brilliantly academically, outshining the native born Americans.
This story has been repeated time and again.
The Singapore Chinese outshine the indiginous Malaysians.
The Filipino Chinese are at the top of Filipino business (one of my Chinese friends said, "We are the Jews of Asia".)
The Hong Kong Chinese score better than mainlanders.
I've heard that we don't have to look overseas to see this... Silicon Valley kids and Los Alamos kids also score well on IQ tests... ok, maybe it's from smart parents, but many people are transferred into Silicon Valley and Los Alamos - it would be interesting to compare the native born kids with the imports from other states...