One more thing about Samuelson's article. He says that high-skilled immigrants assimilate more quickly than low-skilled immigrants. Is this true?
Samuelson refers to all sorts of economic data to make his case, but I don't think assimilation is necessarily related to earnings. It's more about your sense of who you are. In fact, I think a case could be made that low-skilled immigrants who are given a genuine opportunity to become full Americans will grab that chance more firmly than those who enter the country with high skills and/or college degrees.
I don't have any hard evidence either, but I'm not sold that it's as straight-forward as Samuelson claims. You only have to spend a short while on a European college campus to realize that most students who pass through will have been exposed to high levels of anti-Americanism. One can absorb an awful lot of that and still want to go to America to earn a high wage. I'm not sure, however, that they'd necessarily assimilate as willingly as someone who only wants a chance for his children to have a better life than he had.