International science education reforms seek to support teachers in using everyday assessment to draw out and work with student ideas; however, developing these instructional practices requires time and support. This paper investigates how a professional development program supported high school chemistry teachers to learn about formative assessment design with a learning progression for modelling energy. Five high school chemistry teachers participated over the course of one academic year, attending bimonthly school-based sessions in which they designed, enacted, and reflected upon formative assessment tasks. We used qualitative methods to analyze recordings of professional development meetings, videorecorded classroom observations, and interviews. Findings suggest that the professional development approach supported teachers' learning about tools and routines of formative assessment with the learning progression, and in turn, they were able to apply this learning in their classroom practice.