This study investigates pedagogical disagreements about assessment in teacher team meetings. Combining quantitative and micro-ethnographic discourse analysis, we explore the characteristics of teachers' disagreements about assessment and the conditions that afford or constrain their development as productive for teacher on-the-job learning. We analyse 149 disagreements from 46 team meetings and explore two contrasting case studies. We find that disagreements about assessment last longer than other disagreements; they more often involve high-stakes decision-making processes; and they tend to be more disputative than disagreements about other topics. The analyses highlight, on the one hand, the potential advantages of disagreements about assessment for teacher learning. On the other hand, the analysis indicates that, to realise this potential of assessment disagreements, teachers need to acknowledge the volatile nature of these disagreements, to productively manage power relations, and to refrain from intensive engagement in micropolitics.