There is growing interest in using comparative judgement to assess student work as an alternative to traditional marking. Comparative judgement requires no rubrics and is instead grounded in experts making pairwise judgements about the relative 'quality' of students' work according to a high level criterion. The resulting decision data are fitted to a statistical model to produce a score for each student. Cited benefits of comparative judgement over traditional methods include increased reliability, validity and efficiency of assessment processes. We investigated whether such claims apply to summative statistics and English assessments in New Zealand. Experts comparatively judged students' responses to two national assessment tasks, and the reliability and validity of the outcomes were explored using standard techniques. We present evidence that the comparative judgement process efficiently produced reliable and valid assessment outcomes. We consider the limitations of the study, and make suggestions for further research and potential applications.