The vexed question of how and why some pedagogical practices persist and others do not lies at the heart of sustaining changes that enhance teaching quality. Understanding the role that leadership practices can play in this process is crucial: schools play decisive roles in allocating life chances for young people. This paper draws on findings from a qualitative parallel case study of two Australian Catholic high schools which examines the contrasting approaches to school change that the schools adopted as they implemented major school-based initiatives to enhance students' academic and social outcomes. It identifies the kinds of practice conditions that permit changes to teaching practices to be sustained in high schools in an era of increasing accountability and student diversity.