Schooling improvement initiatives have demonstrated that moderate but significant achievement gains are possible with well designed interventions, but there is little research into whether these gains can be sustained. The present study examines the extent to which acceleration in achievement made during a three-year literacy intervention and the associated school-based practices were continued. Statistical modelling showed continued acceleration in student achievement (four months in addition to expected progress) at a rate similar to the intervention. The school-based practices associated with sustainability were part of a process of change (rather than a specific instructional programme) comprising two dimensions--organisational learning through ongoing inquiry into solving problems arising from teaching and learning and the development of professional learning communities to promote organisational learning. Effectiveness was enhanced by schools embedding the process into their normal school routines as part of a coherent instructional programme and the availability of expertise.