The authors drew upon Remillard and Bryans' categorization of curriculum use in observating two middle-grade teachers' integration of Standards-based curriculum materials produced by the National Council of Teachers of Mathematics. Each teacher participated in a two-year professional development program focused on increasing content knowledge and pedagogical content knowledge, and fostering the development of communities of practice within each school. Results indicated that the site-based communities of practice afforded one teacher continued opportunities to reflect upon and critique instructional decisions, whereas the lack of a community of practice at another school limited the teacher's integration of the materials into the instruction.