This research examines secondary mathematics teachers' use of textbook curriculum materials within "typical" cycles of planning and teaching in a school year. The curriculum use of four teachers from the western US was examined before and after engagement in a form of professional development focused on more purposeful and flexible curriculum use. A multiple case study approach was used in order to uncover and describe patterns of curriculum use over time in greater detail. Planning and teaching materials were collected, grouped, and coded for reflectivity of more effective adaptations. Overall, the number of textbook materials teachers used "as-is" dropped dramatically while the number of materials they "adapted" increased. This finding was true regardless of teaching experience, teaching context, textbook used, or content taught. Furthermore, the types of adaptations teachers made to their curricula were more deliberate and student-specific in the spring than they were in the beginning of the school year. This research sits within the broader domain of understanding how mathematics teachers use curriculum and raises new questions about how, when, and why teachers make changes to textbook materials. (Contains 2 tables, 4 figures, and 2 notes.)