Remedial or developmental courses are the most common policy instruments used to assist underprepared postsecondary students who are not ready for college-level coursework. However, despite its important role in higher education and its substantial costs, there is little rigorous evidence on the effectiveness of college remediation on the outcomes of students. This study uses a detailed dataset to identify the causal effect of remediation on the educational outcomes of nearly 100,000 college students in Florida, an important state that reflects broader national trends in remediation policy and student diversity. Moreover, using a Regression Discontinuity design, we discuss concerns about endogenous sorting around the policy cutoff, which poses a threat to the assumptions of the model in multiple research contexts. To address this concern, we implement methods proposed by McCrary (2008) and discuss the strengths of this approach. The results suggest math and reading remedial courses have mixed benefits. Being assigned to remediation appears to increase persistence to the second year and the total number of credits completed for students on the margin of passing out of the requirement, but it does not increase the completion of college-level credits or eventual degree completion. Taken together, the results suggest that remediation might promote early persistence in college, but it does not necessarily help students on the margin of passing the placement cutoff make long-term progress toward earning a degree. (Contains 5 tables and 4 figures.) [This publication was produced by the National Center for Postsecondary Research.]