"In Brief" focuses on K-12 mathematics and science research and implications for policymakers, educators, and researchers seeking to improve student learning and achievement This brief highlights the learning gains of 240 elementary students involved in a long-term study in Madison, Wisconsin and their remarkable ability to reason with arithmetic in ways that build their capacity for algebraic reasoning. The research summarized in this article shows that with appropriate teacher professional development, teachers can learn to help students learn mathematics in ways that both enhance their understanding of arithmetic and provide a foundation for learning algebra. Teaching and policy considerations for learning algebra in the elementary grades are attached. (ASK)