This article explores the features relating to the validity of assessment for learning, in particular the features of a "collaborative" assessment for learning, because of the learning benefits associated with collaborative learning. The article indicates what some of the learning benefits of highly valid collaborative assessment for learning might be, assuming that a valid assessment for learning "actually" promotes learning. It explores the idea that, for an assessment for learning to be valid, its learning outcomes must be socially appropriate for learners of the twenty-first century. The article illustrates some of these conceptual points, using descriptions of three collaborative assessments for learning currently being practised. Two of the illustrations are taken from the UK and one from the Eastern Caribbean. (Contains 1 note.)