In this article, I investigate the influence of the dominant culture characterizing mathematics education--which I term the "culture of exclusion"--on efforts to teach for equity. Analyzing a year of observations in an urban high school mathematics department, I found that this culture structured everyday instruction even for teachers who expressed strong commitment to equity and who participated in ongoing equity oriented professional development. Through their classroom practice, the 4 focal teachers in this study often framed mathematics as a fixed body of knowledge to be received, and they positioned students as deficient, unintentionally excluding many students from rich learning opportunities. However, these teachers also asserted alternatives to the culture of exclusion, showing how resistance to this culture might take shape in everyday mathematics instruction.