School leadership theory has evolved since the 1980s from the traditional, hierarchical model to a democratic vision of leadership as an organizational phenomenon (Ogawa & Bossert, 1995). When classroom teachers are engaged in leadership activities, collective empowerment takes root and teachers' commitment to school goals increases. The purpose of this study was to investigate teachers' current and desired practice of teacher leadership. This study also investigated the relationship between teacher leadership and principals' practice of transformational leadership. Six hundred twenty-five teachers from ten of the thirteen Bucks County school districts participated in this study. The findings in this study suggest that for the teachers who participated in this study phase three teacher leadership is more widely practiced than anticipated. Furthermore, when given the choice most teachers would either continue practicing phase three teacher leadership or they would like to begin practicing phase three teacher leadership. This study also found that teachers' years of teaching experience is not an accurate predictor of phase three teacher leadership. This study did not find a relationship between the practice of teacher leadership and principals' practice of transformational leadership. Further investigation is recommended to investigate other models of principal leadership that may enhance phase three teacher leadership. Further investigation of phase three teacher leadership is also recommended to determine how teachers find time to engage in phase three teacher leadership tasks and how their principals support their work. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]