Low-performing high schools serving disadvantaged students are more likely to have less experienced and less knowledgeable teachers than other schools. MDRC’s recent evaluations of three high school reform models — Career Academies, First Things First, and Talent Development — have addressed questions about how to improve the content and delivery of what is taught in high schools through the use of new curricula and through professional development. Together, these studies suggest that structural changes to improve personalization (for instance, creating small learning communities) and instructional improvement are the twin pillars of high school reform. While only limited data are available linking instructional improvement efforts to changes in student outcomes, the experiences of program developers and of participating schools and teachers suggest a number of operational lessons about putting instructional improvement efforts in place