This research guide from the Center on Reinventing Public Education explores the history and approaches to math instruction in U.S. schools. Debates about traditional and reform sides of the “Math Wars” have existed since the early 1900s, informing the divide in math education today. Instead of endorsing one approach over another, the guide explores the instructional differences between “traditionalist” and “reformer” stances that either prioritize procedural fluency or conceptual understanding. Moreover, the guide shares findings about what approaches math teachers are using in their classrooms, pointing out that many teachers often default to worksheets and lectures rather than recommendations from either approach. The guide concludes with recommendations for state and district leaders to enhance math instruction by drawing upon the strengths of diverse approaches. Math instructional coaches and department chairs may find this guide useful, as it offers tangible steps to improving students’ and teachers’ access to high-quality math instruction.