This report details the findings from an eight-year, longitudinal impact study of the Bill & Melinda Gates Foundation's Early College High School Initiative (ECHSI). The authors introduce ECHSI and provide an overview of Early College High Schools, pointing out that Early College High Schools are unique, offering supports that specifically provide students with a foundation from which to launch their postsecondary career. These supports include a curriculum that provides one to two years of transferable college credit, integration into and partnership with an existing higher education community, and assistance with the application and transition to college. The study design utilized random assignments to evaluate and compare a large sample of Early College High School and traditional high school students. The authors found that Early College High School students were six percent more likely to graduate from high school, 13 percent more likely to enroll in college, and were eleven times more likely to earn a postsecondary degree (22 percent versus 2 percent; with 20 percent earning a degree upon high school graduation) within 2-4 years post-graduation.