This paper addresses the question of how classroom-based peer assessment practices can be improved in relation to student interpretations of subjective assessment criteria. To achieve this, this research study considers the possible pedagogic benefits and implications of using a comparative judgement (CJ) approach to the peer assessment of GCSE English students' creative writing. The study was conducted through a series of workshops in which students acted as peer assessors and made decisions on what constituted good-quality creative writing. Students then participated in interviews that gave insight into their assessment decisions. Findings suggest that students draw on internalised quality markers that exist in tacit form when peer-assessing through comparative judgement and that a collaborative and dialogic approach to the understanding and sharing of these is crucial if high quality learning through peer assessment is to be fostered and maintained.