Numerous studies show the positive effects of a growth mindset on students' learning. Little has been said about the role teachers' mindsets play for school improvement. In this study, the authors analyzed whether growth mindsets of teachers (vs. fixed mindsets) have an influence on: (1) the interest in their professional development; (2) their organizational cognitive and emotional-motivational regulation; and (3) their individual perception of whether their schools are on the right track to improve. Multilevel SEM analyses on a sample of Swiss primary school teachers (N=1625) reveal that a growth mindset has a positive effect on the perception of the school's improvement. Furthermore, this effect is mediated through organizational cognitive and emotional-motivational regulation and interest in professional development.