To date, there is little or no research that specifically examines assessment literacy in social studies education, or the relationship between preservice teachers assessment literacy and their thinking about their own agency. This article focuses on three preservice social studies teachers who demonstrated a high degree of assessment literacy in their lesson plans, by developing assessments that supported their purpose for teaching social studies and their instructional decisions. The preservice teachers' thinking about their assessment decisions in their field experience classrooms was examined through artifacts, interviews, and reflections. The preservice teachers' thinking demonstrated that their assessment literacy was distinct based upon their views of the teaching profession. The findings from this case study highlight the ways that the authoritative discourses of assessment can influence the agency of preservice teachers. The discussion of findings highlights several implications for social studies teacher education.