  We report on progress towards the development of an Action Concept Inventory
(ACI), a test that measures student understanding of action principles in
introductory mechanics and optics. The ACI also covers key concepts of
many-paths quantum mechanics, from which classical action physics arises. We
used a multi-stage iterative development cycle for incorporating expert and
student feedback into successive revisions of the ACI. The student feedback,
including think-aloud interviews, enabled us to identify their misconceptions
about action physics.
