This qualitative study was designed to examine teachers' and principals' perceptions of the impact of a graduate program designed to prepare teacher leaders. Impact was investigated through interviews with 20 graduates and 6 principals. Using Mezirow's concept of transformational learning, the study documents perceived transformation of teachers' frames of reference: two related to teaching (adopt an inquiry stance; learn to view oneself as an autonomous professional), and two related to leadership (adopt a leadership stance; view student learning as a communal responsibility). The study includes implications for the design of graduate level teacher education programs to enhance their impact and effectiveness.