This study explores the concept of school evaluation and in particular how the Irish education system and post-primary schools can successfully move from a centrally controlled system of evaluation to a model based on school self-evaluation. Within a context of increasing interest in school evaluation nationally and internationally, the relationship between evaluation, decentralised decision making and increased school autonomy is discussed. The purpose of evaluation and its importance in fulfilling accountability and improvement needs is acknowledged. The impact of the introduction of whole-school evaluation (WSE), as a model of external evaluation, on schools whose quality assurance heretofore was assessed predominantly through state examinations is investigated. The formal introduction of internal evaluation to schools in Ireland, advanced through recent social partnership agreements, anticipates that schools will assess their teaching and learning practices through the use of a specific framework. The extent to which post-primary schools engage in internal evaluation and the support required to enhance this is examined. The experience of key personnel in the Irish education system was explored to increase knowledge and gain deeper understanding of school evaluation and its impact on the quality of education provided. Reflections and insights of inspectors who take responsibility for external evaluation, of support service personnel who provide support for school leadership and for school development planning, and of principals of post-primary schools were obtained through the use of focus groups. Their views were analysed using a number of themes. In particular, the role of evaluation in creating schools as learning organisations was investigated. The absence of teachers’ voices in particular, and of students’ and parents’ voices, is acknowledged as a limitation in the study. Results of the research indicate that support provided to assist schools to engage in school development planning, combined with the experience, support and pressure of external WSE, has laid the foundation for the introduction of internal evaluation. Collaborative improvement processes have been initiated, on which internal evaluation can be based. While aspects of external evaluation are criticised, there is general acceptance that a model that balances external and internal evaluation is desirable. The need for clear guidelines and appropriate support is stressed. Crucially, the model of internal evaluation proposed is one of reflection and inquiry, using suitable benchmarks and data, and taking account of context to ensure that evaluation assists schools in becoming learning organisations.