We investigated how 53 elementary teachers interpreted the impact of the contexts in which they work on their mathematics instruction, and what those interpretations reveal about the agency individual teachers were able to achieve. Latent class analysis revealed two distinct classes, with teachers in one class perceiving that their contexts had a greater and more supportive impact than teachers in the other class. Interviews of four elementary mathematics specialists then revealed that the extent to which agency was achieved depended on not only their evaluations of the constraints and affordances of their contexts, but also their past experiences and future goals. [For the complete proceedings, see ED629884.]