Given the recent attention on early childhood mathematics education, it is important to understand how early childhood educators conceptualize the work of mathematics teaching and learning. This article describes a study of preschool educators’ conceptions of mathematics teaching and learning in the context of a multi-year professional development project at two Head Start preschool centers. In particular, I examined how participants in this study perceived their roles in mathematics teaching and learning, and how their conceptions demonstrated awareness of children’s ways of thinking and learning in play. I found that educators’ conceptions converged around three themes of practice: 1) engaging and nurturing, 2) noticing children’s mathematical activity, and 3) guiding children’s mathematical learning. These conceptions shed new light on the promises and challenges of professional development aimed at improving mathematics teaching and learning in early childhood education.