Despite decades of policy intervention to increase college entry and success among low-income students, considerable gaps by socioeconomic status remain. To date, policymakers have overlooked the summer after high school as an important time period in students' transition to college, yet recent research documents high rates of summer attrition from the college pipeline among college-intending high school graduates, a phenomenon we refer to as "summer melt." We report on two randomized trials investigating efforts to mitigate summer melt. Offering college-intending graduates two to three hours of summer support increased enrollment by 3 percentage points overall, and by 8 to 12 percentage points among low-income students, at a cost of $100 to $200 per student. Further, summer support has lasting impacts on persistence several semesters into college.