This article provides an example of, and lessons from, teaching and learning critical mathematics in a Chicago public neighborhood high school with a social justice focus. It is based on a qualitative study of my untracked, 12th-grade mathematics class, a full-year enactment of mathematics for social and racial justice. Students were Black and Latin@ from a low-income, working-class community with a tradition of resistance. Any neighborhood student could enroll without selection criteria. The class goal was for students to cocreate a classroom in which they would learn and use college-preparatory, conceptually based mathematics to study and understand social reality to prepare themselves to change it. Through analyzing my practice, I address possibilities and challenges of curriculum development and teaching, examine student learning, and pose questions and directions for further research and practice.