As curriculum standardization escalates, teachers' agency in relation to teaching to student diversity takes on increasing importance. This article draws from an international study that investigated the multicultural and antiracist teaching practices of 15 English teachers in two racially diverse schools, one in the United States, the other in Canada. Analysis of in-depth interviews and curriculum-related documents found that teachers' agency was related to biographical elements of professional preparation, prior experiences with diversity, and generational status. The article reports on data from the United States school and offers recommendations for professional development and teacher preparation. (Contains 1 table.)