This study examined the effects of professional development on teachers' assessment literacy between two groups of teachers: (1) teachers who were involved in ongoing and sustained professional development in designing authentic classroom assessment and rubrics; and (2) teachers who were given only short-term, one-shot professional development workshops in authentic assessment. The participating teachers taught Year 4 and 5 English, science, and mathematics. The findings showed that the assessment literacy of teachers who were involved in ongoing, sustained professional development had increased significantly during the second year of study. These teachers had also gained a better understanding of authentic assessment. (Contains 6 tables.)