In the wake of the federal No Child Left Behind legislation, standardized tests have become increasingly high-stakes. Yet English language learners (ELLs) typically score far below native English speakers, creating pressure to "teach to the test." This article shares findings from an intensive year long study in 10 New York City high schools, detailing how high-stakes tests become "de facto" language policy in schools. Most schools and individual educators have increased the amount of English instruction ELLs receive; however, some have instead increased native language instruction as a test preparation strategy. Curriculum and instruction focuses on test content and strategies, and English as a second language classes have become more like English language arts classes for native English speakers. In bilingual classes, tests are found to promote monolingual instruction with test translations guiding decisions about language allocation. (Contains 2 endnotes.)