In the wake of recent federal legislation entitled No Child Left Behind, high-stakes standardized testing for accountability purposes is being emphasized in educational systems across the U.S. for all students – including English Language Learners (ELLs). Yet language proficiency mediates test performance, so ELLs typically receive scores far below those of other students. This book explores how tests have become de facto language policy in schools, shaping what is taught in school, how it is taught, and in what language(s) it is taught. In New York City, while most schools responded to testing by increasing the amount of English instruction offered to ELLs, a few schools have preserved native language instruction instead. Moreover, this research documents how tests are a defining force in the daily lives of ELLs and the educators who serve them.