In previous work, we described how three teachers differentially create opportunities for students to act as epistemic agents and to engage in collective knowledge-building work (Alzen et al., 2020). The descriptive nature of this previous research provided information about what variability can look like in classrooms attempting these reform-oriented pedagogical shifts. In this paper, we extend this prior work by presenting an expanded, but still exploratory analysis of how those three teachers, who participated in the same professional development community and were working with common instructional materials, attempted to support student agency through science practices in a common lesson. Our present goal is to use a multi-case study to identify emerging variations in key elements of knowledge and practice for inviting students' epistemic agency, even as teachers work toward specific learning goals. From these cases we advance the research by building theoretical conjectures that can be explored further in future work about how teachers' choices about collective knowledge building may yield differential opportunities for students to experience epistemic agency. We leverage variation between enactments to explore tensions in enacting reforms. These shifts can be challenging for teachers who naturally interpret new reforms through the lenses of their current knowledge and practices (Spillane et al., 2002). Variations in how classrooms showcase these reforms can help identify the variety of potential tensions with current practice. Contrasting realizations of agency or collective enterprise can help identify those aspects of the reform that are not uniformly taken up and thereby suggest elements of the reform that present greater challenges. For example, perhaps providing opportunities for students to pose their own questions at the start of a unit emerges more consistently across classrooms, while using student questions to motivate target investigations appears more variable. The goal in the current study is to go beyond asking "to what extent did teachers take up a practice such as scientific argumentation" to a more nuanced analysis of how teachers interpreted and attempted to realize the practice in their classrooms. We use our unpacking of epistemic agency and collective enterprise to articulate these more nuanced questions about science practices. To do this, we investigate variations between classrooms in the apparent norms, participant structures, and resulting student activity. We examine how norms are communicated and reinforced through teachers' words and actions. How do teachers communicate to students that the "rules of the game" may be different from their prior experiences? How do teachers persuade students that their initial ideas are important to share, when much of their prior schooling may have led students to believe that they should only volunteer an idea that they are sure is correct? How do teachers convince students that they really mean this commitment to agency and collective enterprise, and it is not "just talk"?