This study examines the impact of attending selective high schools on advanced mathematics course-taking, challenging the assumption that such schools uniformly benefit students, and investigating how selective admissions processes and organizational policies interact to shape students' course-taking patterns. Using student-level data from New York City, the study compares students just above and below selective schools’ admissions cutoffs to evaluate the effects on advanced math course-taking. In general, students admitted near the cutoff are less likely to enroll in advanced math classes compared to those just below the cutoff. This effect is particularly pronounced in schools with restrictive or hierarchical practices, which tend to limit students’ opportunities. Conversely, schools with more inclusive policies foster greater participation in advanced math. Overall, this study highlights the complex interplay of sorting processes between schools and sorting processes within them, challenging the notion that selective schools uniformly confer academic benefits to their students.