Harlem Children's Zone (HCZ), which combines community investments with reform minded charter schools, is one of the most ambitious social experiments to alleviate poverty of our time. We provide the first empirical test of the causal impact of HCZ on educational outcomes, with an eye toward informing the long-standing debate whether schools alone can eliminate the achievement gap or whether the issues that poor children bring to school are too much for educators alone to overcome. Both lottery and instrumental variable identification strategies lead us to the same story: Harlem Children's Zone is effective at increasing the achievement of the poorest minority children. Taken at face value, the effects in middle school are enough to close the black-white achievement gap in mathematics and reduce it by nearly half in English Language Arts. The effects in elementary school close the racial achievement gap in both subjects. We conclude by presenting four pieces of evidence that high-quality schools or high-quality schools coupled with community investments generate the achievement gains. Community investments alone cannot explain the results.