There is a continuing emphasis in the United States on improving students' mathematical abilities, and one approach is to better prepare teachers. To investigate the potential usefulness of Lesson Study to better prepare teachers, one author set out to conduct action research on his classroom practice. Specifically, he sought to determine whether using Lesson Study with preservice secondary mathematics teachers might better prepare students to be teachers. The participants were preservice teachers who were enrolled in a mathematics methods course in an undergraduate teacher preparation program at a private university. The researcher served as a participant observer who implemented an innovation, Lesson Study, in his classroom and observed the effect on students. Lesson Study engaged the preservice teachers in collaboratively creating, field testing, revising, and re-teaching lessons in their field placement classroom. Data were weekly reflections and summative interviews of the preservice teachers. The researcher found that Lesson Study was an effective strategy for enhancing the efficacy of preservice teachers. Action research showed the importance of collaborative lesson preparation, practice teaching, and observations of other teachers. The preservice teachers successfully transitioned from teaching in the methods classroom to their field-experience classroom, which enhanced their confidence as they entered student-teaching.