Children from low-income families face persistent educational and economic disadvantages that contribute to long-run earnings gaps. This paper studies Communities in Schools (CIS), a program that places coordinators in high-poverty schools to connect struggling students with individualized support. CIS is the largest program of its kind in the U.S., serving nearly 2 million students annually. We find that CIS improves test scores, attendance, and behaviour for struggling students, and that these gains persist, leading to higher rates of high school graduation, college attendance, and adult earnings. These long-run effects can be closely forecast from changes in short-run outcomes, with non-cognitive measures playing a central role. CIS delivers returns that compare favourably to other major education interventions, such as class-size reductions. Our results suggest that programs like CIS—combining traditional school resources with mentorship and social capital—can produce lasting improvements in education and economic mobility for disadvantaged students.