This report describes the implementation of the No Child Left Behind (NCLB) Act in school districts and schools with large enrollments of English language learners (ELLs) and immigrant students. The study, part of a series on the education of young immigrant students, documents how this landmark legislation in education policy played out in three high-ELL districts and six schools and traces the law’s effect on the education of ELL students attending these schools. The research, which takes a case study approach, addresses the following questions: 1) How has NCLB been implemented in high-ELL schools? 2) What has been the effect of NCLB on the improvement of high-ELL schools? and 3) What has been the effect of NCLB on ELL students in high-ELL schools? The findings reveal that, while implementation of NCLB in high-LEP schools has resulted in some problems for ELL students’ education, the net effect of the law has been positive because it has increased attention paid to ELL students; increased the alignment of curriculum, instruction, professional development, and testing; and raised the bar for ELL student achievement.