A growing body of research on change within the general context of educational reform (e.g., Borko, et. al., 2000; Richardson, 1994) and physical education (e.g., Rink & Williams, 2003; Ward, 1999) suggests that specific features of interventions, teachers, and institutional contexts facilitate and hinder teacher change. The purpose of this study was to examine the process of change experienced by Kate and Dianne, 2 of 12 middle school physical education teachers that participated in the Assessment Initiative for Middle School Physical Education (AIMS-PE) Project. The purpose of the project was to help teachers examine and reframe their assessment practices and to increase their students’ knowledge and behaviors around physical activity. A comparative case study design was selected because this type of thorough examination of teachers’ experiences is well suited to questions such as what enables teachers to change their materials, practices and beliefs, and what hinders their efforts. Data were collected from formal and informal interviews with teachers, students and project researchers, field notes from observations, and school artifacts. Interview transcripts and field notes were coded using open, axial, and selective coding (Strauss & Corbin, 1998). Three patterns of change were prominent in the teachers’ experiences: (a) increased planning and more efficient organization and management, (b) improved alignment of instruction processes and instructional assessments, and (c) a shift in teacher roles characterized by letting go of control to facilitate student oriented small-sided games and student peer assessments. Kate and Dianne reported that their changes required time, opportunity, and ongoing support, without which positive change could not have been achieved. In their final interviews, the teachers stated that they knew more about what their students understood and could do in physical education than they had in previous years. They identified that project workshop sessions generally were an effective catalyst for change, and that hands-on training in the construction of assessment tools and assistance in the management of assessment were essential during planning and implementation. For these two teachers, change involved risk taking and often appeared messy in the early stages as they departed from what they knew well to try new practices and strategies. Results suggest that it is important for teacher development efforts aimed at changing current physical education to create opportunities for teachers to participate in programs with the intensity, multiple resources, and ongoing support necessary to address the multiple demands expected of teachers by contemporary reform agendas. Keyword(s): professional development, research