In this paper, we present findings from a preliminary analysis of transcript data in the High School Longitudinal Study (HSLS:09), a large-scale longitudinal investigation of academic achievement among U.S. high school students. Using proportional flow diagrams of course-taking patterns, we illustrate differences in calculus completion associated with non-malleable student characteristics such as ethnicity, gender, and socioeconomic status (SES), as well as malleable student characteristics, such as knowledge of mathematics in ninth grade, the level of mathematics course they take in ninth grade, and self-efficacy. Confirming and extending findings from prior literature, we conclude that "tracks" through high school mathematics curriculum, together with students' ethnicity, SES, and self-efficacy, converge as important factors associated with which of the approximately 19% of high school students complete calculus in high school.