Our work concerned the socio-cultural practices of tutors from diverse higher education institutes. The tutors were practising lecturers who had contributed to peer assessment studies published in refereed academic journals. Analysis of interview data considered the relational interdependency of tutors' and students' activity in the socially and culturally structured world of peer assessment. Undertaking peer assessment led to changes in: (1) relational learning between tutors and students, and (2) tutors' and students' perceived identities. The findings are discussed in terms of: (a) learning in communities of practice through boundary interactions with other communities, and (b) the participatory and acquisition metaphors of learning. The wider role of peer assessment in terms of interactions, communications and the balance of learning metaphors in higher education is considered.