Comparative Judgement (CJ) is an evaluation method, typically conducted online, whereby a rank order is constructed, and scores calculated, from judges' pairwise comparisons of performances. CJ has been researched in various educational contexts, though only rarely in English as a Foreign Language (EFL) writing settings, and is generally agreed to be a reliable method of evaluating performances. This study extends the CJ research base to young learner EFL writing contexts and innovates CJ procedures with a novel dimension-based approach. Twenty-seven Austrian EFL educators evaluated 300 young learners' EFL scripts (addressing two task types) from a national examination, using three scoring methods: standard CJ (holistic), CJ by dimensions (our new criteria-based method), and the exam's conventional analytic rating. It was found that both holistic CJ and our dimension-based CJ were reliable methods of evaluating young learners' EFL scripts. Experienced EFL teachers who also have experience with using marking schemes proved to be reliable CJ judges. Moreover, despite the preference of some for the more familiar analytic rating method, teachers displayed higher reliability and shorter decision-making times when using CJ. Benefits of dimension-based CJ for reliable and economical scoring of large-scale young learner EFL writing scripts, and the potential for positive washback, are discussed.