Research in L2 writing contexts has shown developing writers’ beliefs exert a powerful mediating effect on how they respond to written feedback. The mediating role of beliefs is magnified in preparation for high-stakes English writing assessment contexts, where tangible outcomes pivot on successful test performance. The present qualitative case study utilises data from semi-structured interviews to investigate how the beliefs of three self-directed IELTS preparation candidates mediated their affective, behavioural, and cognitive engagement with electronic teacher written feedback across three multi-draft Task 2 rehearsal essays. Utilising a metacognitive conceptual approach (Wenden, 1998), the study identified seven themes: 1) self-concept beliefs regulated engagement, 2) reliance on the expertise of a quality teacher, 3) engagement was mediated by individuals’ learning-to-write beliefs, 4) belief in comprehensive, critical written feedback, 5) feedback deemed transferable was more comprehensively engaged with, 6) entrenched test-taking strategy beliefs hindered engagement, and 7) supplementary self-directed learning activities were considered of limited value. The implications for practitioners of IELTS Writing preparation and the IELTS co-owners are discussed.