Justification is a core mathematics practice. Although its role in the mathematician community has been studied extensively (e.g., Hanna, 2000), we know relatively little about its role in K-12 classrooms. This study was conducted to clarify aspects of justification as a learning practice in middle grades mathematics classrooms. We document the views of 12 middle grades teachers who were working actively to incorporate justification into their classrooms. We further analyze differences between teachers’ purposes and mathematician purposes, and how these differences may reflect the different purposes of the two communities. Implications for mathematics education and teacher development are discussed
