This article examines mathematics instruction and its intersection with culturally relevant teaching in an elementary/middle school in a Mexican American community. The findings are based on a collaborative-research and school-change project involving university researchers, teachers, and the school's principal. On the basis of ethnographic data and an interdisciplinary theoretical framework, we propose a three-part model of culturally relevant mathematics instruction. The 3 components are (a) building on students' informal mathematical knowledge and building on students' cultural and experiential knowledge, (b) developing tools of critical mathematical thinking and critical thinking about knowledge in general, and (c) orientations to students' culture and experience.I was 15 [when I came to the U.S.] The first thing I learned was that I was different. Even with my Latino peers. There are levels of being Mexican. I didn't know how bad it was to be who I was. There were so many pressures from name calling, insults in the street, said aloud because I was so Mexican … I had a lot of anger. It was this anger, and anger at the experiences of my brother in school. We all did not do as well because of the school experiences. That made me want to be a teacher.-Ms. Salinas, a sixth-grade teacher in the school In this article, we hope to contribute to a theory of culturally relevant teaching (Ladson-Billings, 1995) of mathematics in a Mexican immigrant community. Our analysis is based on the ideas and practices of five teachers. The teachers are participating in a school-change project in a public school located in a low-income Mexican American community in a large midwestern U.S. city. The purpose of the project is to help teachers use what they know about their students' culture to improve students' learning of mathematics, and of other subjects as well, and to help students develop critical approaches to knowledge and the tools they will need to be agents