This article reports on a subset of findings that emerged from the Alberta Student Assessment Study in relation to the preservice and in-service development of teacher knowledge of, expertise in, and beliefs underpinning their assessment practices. Findings indicate that, although there has been a lot of attention given to improving assessment, confusion remains for teachers about terminology, principles, and pragmatics that undermine teacher confidence about assessment and making sound judgments about students' work. (Contains 1 figure.)