The principles and practices of formative assessment are widely used to improve the learning outcomes of students. Students' learning may also be improved when these same principles and practices are used to guide their teachers' professional learning. This article has been adapted from the paper Using student assessment for professional learning: focusing on student outcomes to identify teachers' needs, commissioned and published by the Victorian Department of Education and Early Childhood Development. The paper sets out a model for teacher professional learning, in which teachers conduct a cycle of inquiry that combines formative assessment of their students' work with the pursuit of their own professional development.