This study examines changes in secondary mathematics teachers' noticing of argumentation through experiencing a peer-assessment cycle. Sixty-one teachers participated in such a cycle comprised of (a) analyzing a written argumentation classroom situation (ACS) using a report format, (b) collaboratively assessing peers' ACS-reports using an ACS rubric format and providing feedback to peers, (c) receiving feedback from peers and individually refining the initial ACS-reports, and (d) reflecting on their experience. Analysis of teachers' initial and refined ACS-reports revealed changes in teachers' noticing of various dimensions associated with argumentation. Analysis of teachers' written reflections and semi-structured interviews provided insights into the characteristics of the experience that supported or inhibited the change in their noticing of argumentation, from their perspective. The study provides evidence of the potential of the peer-assessment-cycle process for teachers' learning to notice key aspects of argumentation.