This qualitative phenomenological study explored the impact of the professional development model, "Powerful Teaching and Learning" (PTL) on teachers' sense of efficacy of 17 secondary teachers at a single high school in Washington State. Qualitative data was collected through in-depth interviews and analyzed using the methodical structure of human science research as presented by Van Manen (1997). Eight themes emerged from the data highlighting the lived experiences of teachers participating in the PTL model: (a) work environments strengthen teachers' commitments, (b) teachers value opportunities to observe other teachers, (c) protocols focus professional learning, (d) observations validate teachers' work and learning, (e) debriefing and reflection ensure teachers' learning, (f) PTL provides a foundation for professional learning communities (PLCs), (g) PTL influences change in classroom practices, and (h) PTL experience perceived as beneficial. Results suggest that the PTL model has the potential to impact teachers' sense of efficacy through professional learning activities that integrate the four sources of efficacy identified by Bandura (1995): validation of mastery experiences, vicarious models of teaching, social persuasion, and emotional arousal. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]