This article aims to explain the role principals play in the variation in academic achievement between secondary schools in Hong Kong. The article draws on survey data from 179 key staff and 2,037 students from 42 schools. The study uses 2 analytical approaches. First, it employs classification and regression tree analysis (CART). This was used to sort out the most significant leadership practices associated with student achievement. Second, based on first-stage analysis, the study further explores the effects of leadership practices on academic achievement using hierarchical linear modelling (HLM). Results indicate that transparent and efficient communication structures as managed by principals explained approximately 12% of between-schools variation in academic achievement. Leadership practices related to quality assurance and accountability and resource management also contributed to explaining between-schools variation in academic achievement, yet they had negative effects on student achievement. Implications for research and practice are discussed.