We study the effects of access to high school math and science courses on postsecondary STEM enrollment and degree attainment using administrative microdata from Missouri. Our data panel includes over 140,000 students from 14 cohorts entering the 4-year public university system. The effects of high school course access are identified by exploiting plausibly exogenous variation in course offerings within high schools over time. We find that differential access to high school courses does not affect postsecondary STEM enrollment or degree attainment. Our null results are estimated precisely enough to rule out moderate impacts.