School climate is critical to school effectiveness, but there is limited large-scale data available to examine the magnitude and nature of the relationship between school climate and school improvement. Drawing on statewide administrative data linked with unique teacher survey data in Michigan, we examine whether school climate appeared to play a role in the effects of a state-level school turnaround intervention. Using comparative interrupted time series models and descriptive mediation analysis, we find that students in schools with more positive school climate appeared to fare better than their peers in schools with less positive climate. Certain elements of climate—relational trust and school leadership—also mediated the effect of turnaround on student achievement. Our findings have implications for school improvement planning, for the design of evaluations of school turnaround initiatives, and for data collection by states aiming to improve their lowest performing schools.