This paper reports on empirical research into formative assessment conducted in a blended learning environment within a professional doctorate in education (EdD.) programme in an English university, focusing primarily on peer discussion forum activity. This was conceptualised within sociocultural learning theories, where learning entails processes of identity formation. The data presented suggests the usefulness of online environments for supporting students' development of subject positions as researchers, thereby constructing new relations between peers, as well as tutors and students, in addition to providing shared textual resources upon which the tutor's feedback can then build. The paper discusses how this might contribute towards more collective forms of doctoral supervision. (Contains 2 figures and 1 note.)