In April 2000 the state of North Carolina announced an increase in the minimum number of math courses students would need to take to be considered for admission as undergraduates to any of the University of North Carolina's 15 four-year branch campuses. Previously, students had been required to take at least three math courses in high school to be eligible for admission. The new standard required at least four math courses and applied to all students graduating from high school in the 2005-06 school year or after. The state justified this increase in required math preparation by arguing that it would improve college completion rates. The purpose of this paper is to assess the effects of this increase in the mandated minimum number of math courses. This assessment entails two separate questions: (1) Did the policy affect actual course-taking among high school students; and (2) Did any such changes in high school course-taking, together with the threat of being denied admission, affect college enrollment patterns or students' choices or performance once enrolled. The study extends the existing literature in three ways. First, it sheds light on how a policy change at the university level affects the behavior of students in high school. Second, it extends the literature on the effects of math taking in high school to college enrollment and college success. Third it makes a methodological contribution by its close attention to the estimation of causal relationships that leverage the plausibly exogenous variation that arises as a result of the policy change.