Teacher professional development (PD) is often an underutilized resource for reform in K-12 schools, and ineffective models often limit the organizational improvements that can be made. In this Action Research report, teachers' experiences with PD at the research site were analyzed using qualitative methods to determine what components of learning are absent. After identifying the need for more collaboration, distributed learning, and the application of adult learning theory, Lesson Study, a cyclical form of learning in which teachers research and plan lessons together, and then engage in lesson delivery and reflection, was implemented as a new model in the action step portion of the research. The results showed that after participants collaborated during multiple cycles, Lesson Study demonstrated positive experiences and results. Further, pre- and post-action step interviews revealed teachers' positive perceptions of the experience. Lesson analysis showed positive effects on classroom practice, and student data revealed a positive effect on achievement. The researcher argues that the voice of the professional teacher must be represented more in PD for true changes in practice to occur. [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.]