This casebook is intended to support professionals who are working in a variety of contexts to use classroom-based assessment more effectively to support teacher learning and teaching change, and to enhance the opportunities for all students to develop mathematical power. It grows out of a collaboration of mathematics teachers and teacher educators, and mathematicians, to better understand the role of assessment as an ongoing activity to help teachers reshape their own teaching practices. At the heart of each case is using assessment to make sense of what students understand and what they are...