Collaboration is a complex construct and collaborative assignments at university are no easy thing to assess. Various approaches have been proposed, mainly addressing formative assessment of collaborative assignments. When it comes to summative assessment, less has been said. This paper presents the findings of a constructivist Grounded Theory (GT) study into English for Academic Purposes (EAP) practitioners’ evaluations of four different models of assessment for a group essay assignment. These evaluations consider the use of various assessment lenses to assess student collaborative work: assessing the product, assessing individual complementary assignments, and assessing the collaboration itself through measures like observation, teacher/group meetings, self- and peer-assessment, and learner reflection. Participants provided sound rationales for and against each assessment approach, further illustrating the complexity of assessing student collaboration. While assessing the product and individual complementary assignments found most favour, there was a clear appetite for assessing collaboration itself, even though there was no clear means of doing so. Although there is not a single assessment approach to collaboration which will fit all circumstances, a multi-lens approach, where assessment lenses are selected on the basis of course learning outcomes and potential learning gains, would allow for fully rationalised assessment schemes.