In this article on a great program to help immigrants in Philadelphia learn English we learn a startling fact (emphasis mine):
The stakes are high. Immigrant students tend to stay in school and graduate, said Ana Sainz de la Pena, who directs English as a Second Language and bilingual education for the district. By contrast, many American-born English language learners struggle and drop out.
I knew we should be concentrating our efforts on those recalcitrant non-English speakers who are already citizens!