When teachers engage in forms of science teaching that disrupt the status quo of typical school science practices, they often experience dilemmas as problems of practice that are difficult--or even impossible--to solve. This instrumental case study examines one teacher's efforts to teach science for equity across two contexts: a public middle school and a summer program for low-income students of color. By tracing intersecting tensions experienced when trying to teach science more equitably, we describe how systems of tensions can serve multiple functions: (1) as roadblocks for teachers when knowledge-production predicaments arise, (2) as dilemmas to be managed by teachers when there is difficulty defining educational disparities, and (3) as potentially productive as teachers and educational researchers wrestle with inherent tensions between models for teaching. Findings afford insight into why teachers experience uneven progress as they work to teach science for equity. Further examination of tensions teaching science for equity reveals deep paradoxes extending beyond the case of a single teacher into pedagogical frameworks underlying expectations for teaching science more equitably in schools.