There are indications that teachers' feedback practice is related to beliefs they hold about pupils' learning and the purpose of feedback. This article presents changes in beliefs and practices of three teachers in lower secondary school taking part in an intervention to improve formative classroom feedback. Data includes interviews, observations and workshop dialogues with the teachers, plus interviews with six pupils (two for each teacher) taking place pre- and post-intervention. Results describe different trajectories, tracing changes in underlying beliefs that highlight the complexity of professional learning as well as the importance of tailoring interventions. The discussion addresses theoretical perspectives of change among teachers and elaborates on results in relation to professional workplace learning.