Transformational leadership by the principal appears to be a precondition of shared instructional leadership in schools, but it does not guarantee that principals and teachers will collaborate on curriculum and instruction. The present study, a content analysis of existing case studies, explores the ways in which teachers respond to transformational leadership by the principal, with attention paid to the influence and conditions that activate interdependent relationships and enhance shared transformational leadership and shared instructional leadership. A contrast school, where shared instructional leadership did not take hold, suggests that structures and processes that organize teachers' work differently do not automatically result in the kinds of interactions associated with quality teaching and learning. (Contains 3 notes and 1 figure.)