Across the United States, more than half of entering freshmen discover they are ineligible for college-level coursework each year, most commonly in math. The readiness gap is widest when considering students at nonselective two-year colleges, and students who are black, Hispanic, or from low-income families. It often spells disaster for students looking to earn a degree: among community college students needing remediation, an estimated 30 percent do not ever enroll in required remedial courses, most do not pass the courses they do take, and just 1 in 10 graduates within three years. How can colleges and policymakers better support students assigned to remediation and improve their rates of college completion? One way would be to boost pass rates in remedial math courses, which may be the single largest academic barrier to college success. Colleges across the country are also experimenting with interventions such as mainstreaming, whereby students assessed as needing remediation are placed directly into a college-level course, sometimes with additional academic support. Although prior studies of mainstreaming have produced mixed results, none have used experimental methods to gain a clear picture of its effectiveness. This article presents new results from a randomized controlled trial of mainstreaming at three community colleges at the City University of New York (CUNY). Some entering students who ordinarily would have been assigned to a remedial elementary-algebra class were placed instead in a college-level statistics course and provided with extra academic support. Findings show that the students placed directly in college-level statistics did far better than their counterparts in remedial classes, even when students in remedial classes were also given extra support. They were more likely to pass their initial math course and, three semesters after the experiment, had completed more college credits overall. This study suggests that many students consigned to remediation can pass credit-bearing quantitative courses right away.