School effectiveness research and school improvement research are central in this article. Based on a study of the literature, the hypothesis is put forward that merging both research traditions might be favourable to fostering the quality of education. A theoretical model is developed for School Improvement in terms of Performance Indicators (SIPI). This model is linked to the Flemish school effectiveness approach that is based on the CIPO model in which Context, Input, Process and Output indicators are distinguished. A central issue in the SIPI model is the use of performance indicators and the way schools receive feedback when participating in performance indicator studies, such as the Programme for International Student Assessment or the Third International Mathematics and Science Study. The paper concludes with the outlining of the number of conditions that have to be met at school level to improve educational quality.