The current age of standardization and accountability in education presents a need for educators to be proficient consumers and producers of data. To understand what mathematics teachers see as the purpose of data and assessment, as well as their perceived needs in these areas, we administered a survey to all mathematics teachers in two school districts in the Midwest. We analyzed perceptions of the purpose of assessment using a framework that breaks from the common formative/summative divide and considers the purpose(s) for assessment as being nuanced and potentially multi-faceted. The responding teachers demonstrated a robust working knowledge of assessment focusing on purposes that serve students, teachers, schools, and states. Responses also indicated that there are gaps in connecting the purposes of assessment and their knowledge on how to implement assessments in ways that meet these purposes. [For the complete proceedings, see ED583608.]