RFA's three-year mixed methods evaluation of Children's Literacy Initiative's language and literacy supports found positive impacts despite higher-than-typical teacher turnover. In pre-K centers receiving CLI supports, teachers were more able to implement effective instructional practices and created richer classroom literacy environments, and children's vocabulary grew faster by an order of magnitude of two-and-a-half months, relative to teachers and children in similar pre-K centers. We observed these impacts consistently throughout the study even though year-to year teacher turnover was higher than national averages. We found that challenges associated with the high turnover inhibited consistently robust implementation of the CLI's intervention. Fewer than one in five teachers received the full intended level of support, and less than half of surveyed teachers reported implementing with fidelity all three of the key instructional approaches of the Blueprint for Early Literacy curriculum supplement (Message Time Plus, Intentional Read Aloud, and Power of Three). Despite variable dosage, the study finds statistically significant positive impact for student learning and teacher practice. This, along with teacher and center director descriptions of ease of use, suggests that CLI's early language and literacy supports are particularly well-suited for improving quality and outcomes in high-need pre-K environments. [Additional funding for Blueprint implementation was provided by Boeing Company Charitable Trust, the 25th Century Foundation, the Caroline Alexander Buck Foundation, and the Capital Group Companies.]