Research is needed to understand the impact of high-stakes testing on teachers' practices and consequently on their students, particularly at schools that serve large numbers of low-income students and students of color. In this research study, we examined how a state's annual high-stakes test and administrative mandates influenced the assessment practices of mathematics teachers at a highly diverse urban high school. Among the most compelling findings was that students at Chavez High (a pseudonym) were labeled based upon their test performance, that this label tended to persist at the school, and that instructional decisions were made based upon these labels. This practice of attaching a label to students based upon their performance on the high-stakes test constructed some students as less capable than others in mathematics. Such practices contribute to the historic legacy in the U.S. of denying poor students and students of color access to a challenging education in mathematics.