Research in science education suggests that teachers' beliefs are linked to the use of inquiry-based instruction; teachers holding a constructivist belief are more likely to engage in student-centered activities in the classroom. However, there is currently little research on the ways in which teachers' beliefs change over time, and in particular, the relationship between instructional activities in teacher education programs and their impact on teachers' beliefs. We examined shifts in secondary preservice teachers' belief orientations as they progressed through a science methods course. We found that overall many of the preservice teachers progressed in their orientation beliefs from a teacher-centered orientation to more student-centered orientation. We characterized four trajectories of change or clusters that describe how preservice teachers' beliefs changed over the course of the semester (15 weeks). We also describe the different ways in which preservice teachers reacted to specific instructional activities, and how those activities influenced their belief orientation. In particular, we found that preservice teachers in a cluster that exhibited a particular trajectory (progression or regression toward/away from student-centered belief orientation) reacted differently to some activities compared to preservice teachers in some other clusters. We discuss these shifts as reflecting changes in priorities of beliefs within belief systems. We argue that teacher educators need to think carefully about the interplay of these beliefs when designing activities so that they can respond (i.e., to a reversal in beliefs) during the course rather than waiting until the end.