The extensive use of CAS at upper secondary school in Denmark provides a laboratory for research
on the development of standards for CAS teaching. The poster focuses on action research into
teachers developing lessons and student activities in an ongoing collaboration between university
and high schools on use of CAS in mathematics teaching. Coaches1 mediate design processes,
reflection and documentation, and enable sharing. We discuss coaching as a valuable part of action
research, and how to draw findings from the collaboration.