Thesis advisor: Robert J. Starratt / This case study examined teacher collaboration and teacher change while in the process of differentiating instruction in the area of mathematics in an elementary school. The project included a two-tier professional development opportunity for the staff. Professional development sessions focusing on specific mathematics skills were offered in lieu of traditional faculty meetings and thirteen, teacher volunteers in grades K-3 participated in bi-monthly study groups. The study describes the journey of the thirteen teachers as they identified successful strategies for differentiating instruction to meet the needs of all learners. The study explored how job-embedded professional development offered teachers the resources and support to meet together during the school day to engage in dialogue about their students' progress, difficulties encountered when teaching specific concepts and skills, and proactively planning in order to differentiate instruction effectively. The study focused on collaboration as a method for learning together in an adult learning environment and improving current teacher practices. The research was qualitative with the school principal as both researcher and participant-observer of the study. Data instruments used for the participants involved in this study were pre- and post-implementation surveys of the entire staff, semi-structured interviews of the thirteen teacher volunteers, observations of meetings, teachers' reflective journals, and field notes. Findings indicated that there was an increase in the teachers' use of differentiated instruction in the area of math. While teachers most often differentiated lessons by ability, teachers experimented with differentiating by interest as well as addressing the students' varying learning styles. In addition, teachers found that the embedded study groups were valuable in helping them to collaborate with their peers and improve their practice in teaching mathematics to all learners. In a profession where continual renewal is necessary, it is essential for educators to be provided with adequate time to review current practices, reflect on the strategies that are most successful, and refine their craft in order to provide opportunities that will maximize student thinking and learning. / Thesis (EdD) — Boston College, 2009. / Submitted to: Boston College. Lynch School of Education. / Discipline: Educational Administration and Higher Education.