A significant number of people have very low levels of literacy in many OECD countries. This paper studies a national change in policy and practice in England that refocused the teaching of reading around "synthetic phonics." This was a low-cost intervention that targeted the pedagogy of existing teachers. We evaluate the pilot and first phase of the national rollout. While strong initial effects tend to fade out on average, they persist for those with children with a higher initial propensity to struggle with reading. As a result, this program helped narrow the gap between disadvantaged pupils and other groups.