Half of all college students will enroll in remedial coursework but evidence of its effectiveness is mixed. Using a regression-discontinuity design with data from a large urban community college system, we make three contributions. First, we articulate three alternative hypotheses regarding the potential impacts of remediation. Second, in addition to credits and degree completion we examine several underexplored outcomes, including initial enrollment, grades in subsequent courses, and posttreatment proficiency test scores. Finally, we exploit rich high school background data to examine impact heterogeneity by predicted dropout risk. We find that remedial assignment does little to develop students' skills. But we also find little evidence that it discourages initial enrollment or persistence, except for a subgroup we identify as potentially misassigned to remediation. Instead, the primary effect of remediation appears to be diversionary: students simply take remedial courses instead of college-level courses. These diversionary effects are largest for the lowest-risk students.