This article describes teachers' collective work aimed at learning to teach mathematics for social justice. A situated, sociocultural perspective of learning guides this examination of teachers' negotiation of mathematical goals and social justice goals as they developed, implemented, and revised lessons for social justice. Teacher interviews, discussions, lessons, and written reflections were analyzed using grounded theory methodology, and teachers' conversations were examined concerning the relationship between mathematical goals and social justice goals. Analysis revealed that early tensions arose around balancing these goals, that teachers focused more attention on the social justice component, and that the instantiation of these goals in practice proved difficult. Variables that afford or constrain teachers' roles as social justice educators are discussed, and implications for teacher professional development are suggested.