Learning to use improvement science -- a structured process for planning, implementing, and studying change efforts -- takes time. That time is a worthwhile investment for schools aiming to shift teaching and learning, but it can be a barrier in schools that are often beset by leadership turnover. How can schools, and external partners, address that challenge and help improvement science efforts achieve their potential? This article discusses how, in their work supporting improvement in secondary school literacy practices, the Institute for Learning have discovered the power of teacher leadership to institutionalize knowledge, spread innovation, and maintain the momentum of improvement science efforts.