Hachey's (2013) article celebrates a revolution that is taking place in early childhood mathematics education, fueled in part by developmental research demonstrating the mathematical capabilities of young children. At the same time, Hachey notes that the mathematics revolution she describes is not yet complete. In this commentary, the author considers how developmental research can contribute to further advances in early childhood mathematics education. Specifically, the author identifies two ways in which an understanding of how children's knowledge changes with development and how learning can inform thinking about the objectives of early childhood mathematics education, and about how those objectives can best be achieved.