This study linked ninth-grade student background data and school-reported high school transcript data from the national High School Longitudinal Study of 2009 (HSLS:09) to student item responses on the 2013 National Assessment of Educational Progress (NAEP) mathematics assessment to examine the relationships between high school coursework and end-of-high school mathematics achievement. In a series of marginal maximum likelihood regression analyses, we find that STEM course GPAs, credits earned in AP/IB math and science courses, higher levels of math course content, and course-taking in chemistry and physics are all positively associated with NAEP math achievement. These relationships persist even when gender, race/ethnicity, early grade 9 mathematics achievement, and socioeconomic status are included as covariates. Cluster analysis of students with high estimated achievement suggest multiple paths to high mathematics achievement for students with both high- and low-socioeconomic status backgrounds.