Educators and researchers have long been interested in determinants of access to honors level and college prep courses in high school. Factors influencing access to upper level mathematics courses are particularly important because of the hierarchical and sequential nature of this subject and because students who finish high school with only lower level courses lack readiness for college and have severely diminished chances for admission to college. Our research analyzes a district-level transcript data set. We examine whether probabilities of enrollment in upper level mathematics courses in high school vary by demographic characteristics, before and after controlling for prior achievement. Before controlling for prior achievement, minority and low-income students have significantly lower odds of placement in upper level mathematics courses; after controlling for prior achievement, the disparities disappear. (Contains 2 tables, 1 figure and 7 footnotes.)