Teachers who gather accurate information about student achievement through the use of sound classroom assessment contribute to effective teaching and learning. On the other hand, those who fail to understand and apply the rules of evidence for sound assessment risk doing great harm to students. Thus, all teachers must understand the differences between sound and unsound assessments. This module is designed to promote that understanding. It examines the many users and uses of classroom assessment, the wide range of achievement targets to be assessed, the array of assessment methods teachers use, and the importance of marrying targets and methods in ways that promote sound assessment. Four key attributes of sound assessment are presented for the teachers to apply in their own classroom assessment environments.