This embedded case study examines the leadership practices of eleven teacher leaders in three urban schools to identify how these teacher leaders attempt to change the teaching practice of their colleagues while working as professional learning community leaders and as mentors for new teachers. Using a theoretical framework integrating complex systems theory with Kotter's ("Leading change." Harvard University Press, Cambridge, 1996) eight steps for leading organizational change, we analyze the work and perspectives of individual teacher leaders, and we examine how teams of teacher leaders and principals function collectively in their efforts to lead instructional change. Our findings have implications for schools seeking to utilize teacher leadership as a reform strategy for authentic instructional improvement.