As the national policy community has coalesced around the priority of graduating all students ready for college and careers, the challenge of improving the lowest-performing high schools serving the most challenged populations remains. This policy brief examines the limitations of previous high school reforms and describes new approaches showing promise in producing substantive changes in secondary level teaching and learning. It highlights the central role of school leaders and districts in creating high school learning environments that can engage and support students with widely divergent learning needs. The brief concludes with a set of policy recommendations for the design of coherent systems to build human capital and foster the conditions for high school transformation. (Contains 50 endnotes.)