Recent European and North American government policies, implementing new systems of evaluation and accountability, have highlighted the use of performance data to inform judgments about schools and stimulate school improvement. This has led to the implementation of school self-evaluation considered as an effective means to increase school quality and effectiveness. Decentralization of education systems has promoted a broadening of educational evaluation methodologies and a conceptualization of theoretical approaches and research about school effectiveness and improvement. This study presents a self-evaluation model, called the ISSEMod, thought to improve school accountability, combining central control managed by public authorities (external control) and the autonomy reserved for schools related to pedagogical, instructional and organizational practices (internal control). Using a sample of 58 Tuscan schools, an empirical and explorative model of school self-evaluation focused on a flexible system of areas and indicators to investigate and analyse school quality, is proposed here.