In this study, we used hierarchical linear modeling to examine restricted-use 2011 National Assessment of Educational Progress (NAEP) data to explore relationships between principal-reported time spent on the different NAEP responsibilities of mathematics coaches and specialists (MCSs) and the achievement scores of approximately 37,400 fourth-grade students in 1,500 U.S. elementary schools. The model included adjustments for composite covariates, control variables, and sampling weights. Significant relationships between principal-reported time spent on six different NAEP-defined responsibilities provided by full-time MCSs and fourth-grade students' mathematics achievement were observed, including relationships between achievement and MCSs assisting both teachers and students. Implications for the effective use of MCSs in schools and suggestions for future research are discussed.