This paper argues that research on differential teacher and school effectiveness can be used to explore the relation between quality and equity in education. The results of secondary analyses of 2 studies concerned with effectiveness in different phases of schooling (pre-primary and primary education) are presented. These secondary analyses reveal that the socioeconomic gap in student achievement in each of the 2 core subjects (mathematics and language) tends to be smaller in classrooms and schools that are more effective than others in promoting student learning outcomes (after controlling for prior achievement, socioeconomic status, and gender). Such a relation was not identified when searching for differential teacher and school effectiveness in terms of gender. Implications for research on promoting quality and equity are drawn.