Background or Context: Although a positive school climate is critical to school effectiveness, little is known about whether a focus on school climate may facilitate successful turnaround in the nation's lowest performing schools. The research suggests two distinct but overlapping ways in which climate may explain a turnaround intervention's effectiveness. First, schools with a more positive climate at the outset of reform may be better equipped to enact change under turnaround. Second, a turnaround model that explicitly targets climate may improve school outcomes through improvements to climate, such as by setting a clear mission, clarifying staff roles, and prioritizing working conditions. Purpose, Objective, Research Question, or Focus of Study: We examine whether school climate appeared to play a role in the effects of a state-level school turnaround intervention implemented in about 100 schools over two implementation cohorts in Michigan. Research Design: Drawing on statewide administrative data linked with unique teacher survey data in Michigan, we carry out two sets of analyses. First, we use comparative interrupted time series (CITS) models to examine whether turnaround schools with a more positive climate fared better under turnaround than schools with a more negative climate. Second, we conduct a mediation analysis to explicitly test whether dimensions of climate mediated the relationship between turnaround and student achievement. Conclusions or Recommendations: In our CITS analysis, we find that students in schools with a more positive school climate appeared to fare better than their peers in schools with a less positive climate, particularly in math. Our mediation analysis findings suggest that certain elements of climate--relationships and school leadership--also mediated the relationship between turnaround and 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.