Really? I think American children are actually quite bright. Can you cite your source for saying the immigrant children perform better than the American ones? I went to public schools in the 4th largest city in the nation and that wasn't my experience. We had immigrants from China, Mexico, Cambodia, Vietnam, South America, and South Africa (those are the ones I can remember - it was 30 years ago). With the exception of one chinese kid (who was a wiz at math) everyone seemed about the same. There were smart immigrant kids and smart American kids, there were also stupid immigrant kids and stupid American kids. There was not a higher ratio for either type in either group that I could see.
So what's your source?