Despite advances in educational effectiveness theory and methodology, existing theoretical frameworks of educational effectiveness are only very general, and the embedding of empirically identified results in theoretical models has to be done more systematically. This book contributes to the advancement of educational effectiveness theory by discussing different strategies and by making it clear that the advancement of the theory depends on the advancement of the methodology itself, or in other words: from theory to methodology and from empirical evidence back to theory. This book was originally published as a special issue of School Effectiveness and School Improvement.