In fall 2017, TNTP received a $7.8 million Mid-phase Education Innovation and Research grant from the U.S. Department of Education to implement its Turnaround Leadership Teams Strategy (TLTS), a whole-school reform model that provides training and support to cohorts of principals, school leadership teams, and teachers. Under the grant, TNTP worked with two large school districts in the southeast United States to implement a tailored version of its TLTS program. This evaluation used a randomized controlled trial design in 28 schools to assess the effectiveness of the TLTS program in raising student achievement. After two years of implementation, TLTS had positive effects on student achievement in English language arts (ELA) and math, the two subject areas of focus for TLTS program supports. The effects on students' ELA and math achievement were roughly equivalent to an additional 1.5-2 months of instruction in those subjects. TLTS did not show positive effects on student achievement in other classroom subjects that were not a specific focus of TLTS supports. Null impacts on science achievement and negative impacts on social studies achievement suggest there may have been a tradeoff between core subjects (ELA and math) and non-core subjects (science and social studies). Future research should explore how school reform efforts can avoid such tradeoffs.