To support continuous professional development model in the teaching and learning of mathematics, many districts and schools have begun hiring elementary mathematics coaches and/or specialists (MCSs). However, limited large-scale empirical research exists that determines how the use of MCSs affect student learning and achievement. Kristin E. Harbour and Evthokia Stephanie Saclarides begin to fill in this gap by using data from the National Assessment of Educational Progress to explore the relationship between the presence and responsibilities of elementary MCSs and 4th-grade student achievement in mathematics. Based on their findings, they share practical implications for districts and administrators to consider.