In this article, I provide findings from a multisite case study of three urban high schools. In each of the schools, principals endeavoured to foster the capabilities of their department chairs to enhance school-wide instructional capacity and increase student achievement. Data were gathered from interviews, participant observations and document analyses during a two-year Leadership for Learning grant funded by the Wallace Foundation. The findings highlight the critical role the principals played in cultivating a shared understanding of the need for change; engaging department chairs in authentic instructional leadership initiatives; and providing the ongoing support, resources and commitment necessary for the chairs to enhance their instructional leadership capacities. I conclude the article with implications for research and practice. (Contains 1 figure and 1 note.)