This presentation offers links to numerous research with regard to English language learners. It is from 2006 (not recent but still relevant) and serves as a good comparison with policies and strategies in todays education environment.
NYC still gives English language learners two years (and only two) before they take the standardized ELA exams -- and those students still have to take the NYS math exams which rely on language proficiency in order to take the exam. A conundrum.