Lesson study, a teaching and learning strategy used in Japan, is a new area of consideration for teacher professional development in the United States. An important component of the lesson study process is the role of the facilitator. The intent of this study was to investigate the role of the facilitator in the lesson study process relative to high school teachers' perspectives of content knowledge and pedagogical knowledge in addition to their perspectives of the lesson study process. Educators were prepared as trained lesson study facilitators in a rigorous, state-level professional development training. Untrained facilitators listened to a presentation from a literacy coach at their schools. The Survey of Teacher Perspectives of the Effectiveness of Lesson Study in Improving Teaching and Student Achievement (STEPLS) pretests and posttests were used to evaluate the perspectives of lesson study participants (STEPLS; Wright, 2010). Thirty-six educators from four high schools located in northwest Florida participated in the study. Participant assignment into group was based upon the type of facilitator at each school. The quantitative data analysis of this embedded case study shows mixed outcomes. The impact of a trained facilitator positively influenced the perspectives of pedagogical knowledge for the participants. Moreover, there was an overall improvement for perspectives of lesson study in general for the participants who experienced a trained lesson study facilitator. The facilitator's role appeared to have no influence on perspectives of content knowledge. Results compiled from open-ended questions on the STEPLS and from random interviews generated the qualitative component of this study. The qualitative analysis also showed support for improved pedagogical knowledge. The study results indicate that trained lesson study facilitators are important to ensure high quality lesson study professional development trainings. Trained lesson study facilitators may promote improved pedagogical knowledge of the participants as well as ensure that the lesson study process is effective. [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.]