This paper discusses the challenge of making large-scale improvements in literacy in schools across an entire education system. Despite growing interest and rhetoric, there are very few examples of sustained, large-scale change efforts around school-age literacy. The paper reviews 2 instances of such efforts, in England and Ontario. After describing main features of these reforms, the paper presents 4 main reasons that such efforts are not more frequent: (a) the educational challenge of changing very large numbers of schools and classrooms on a sustained basis, (b) the bureaucratic challenge of improving the connections among different areas of social policy in pursuit of better outcomes for students, (c) the learning challenge of organizing complex systems to do this work while continually modifying the approach in light of new evidence and system feedback, and (d) the political challenge of galvanizing and maintaining the effort required to support these other changes. (Contains 1 note.)