Arts education faces challenges from continual pressure for educational accountability. How should art educators assess inventive and divergent learning in ways that communicate to those outside the arts? The answer matters not only for the development of useful art assessment, but also in securing a place for the arts in public education. Prior assessment efforts are deeply rooted in distinct epistemological stances on the nature of learning and are tied to a particular learning theory, resulting in competing goals that undermine the efforts to document learning from other perspectives. In order to assemble together current assessment efforts through an epistemologically pluralistic approach to assessment, this article uses the metaphor of increasingly formal theatrical staging to review existing and emerging research on arts assessment. Just as the process of "assemblage" lets artists create new meaning from disparate objects, this article introduces a comprehensive new approach, called assessment assemblage theory, for improving "existent" assessment and testing practices to satisfy a range of stakeholders. (Contains 1 table and 3 figures.)