This study examines patterns of literacy instruction in schools adopting three of America's most widely disseminated comprehensive school reform (CSR) programs (the Accelerated Schools Project, America's Choice, and Success for All). Contrary to the view that educational innovations seldom affect teaching practices, the study found large differences in literacy instruction between teachers in America's Choice schools and comparison schools and between teachers in Success for All schools and comparison schools. In contrast, no differences in literacy teaching practices were found between teachers in Accelerated Schools Project schools and comparison schools. On the basis of these findings and our knowledge of the implementation support strategies pursued by the CSR programs under study, we conclude that well-defined and well-specified instructional improvement programs that are strongly supported by on-site facilitators and local leaders who demand fidelity to program designs can produce large changes in teachers' instructional practices. (Contains 6 figures, 7 tables and 8 notes.)