Introduction

Schools are continuously confronted with various forms of change, including changes in students’ demographics, large-scale educational reforms, and accountability policies aimed at improving the quality of education. On the part of the schools, this requires sustained adaptation to, and co-development with, such changes to maintain or improve educational quality. As schools are multilevel, complex, and dynamic organizations, many conditions, factors, actors, and practices, as well as the (loosely coupled) interplay between them, can be involved therein (e.g. professional learning communities, accountability systems, leadership, instruction, stakeholders, etc.). School improvement can thus be understood through theories that are based on knowledge of systematic mechanisms that lead to effective schooling in combination with knowledge of context and path dependencies in individual school improvement journeys. Moreover, because theory-building, measuring, and analysing co-develop, fully understanding the school improvement process requires basic knowledge of the latest methodological and analytical developments and corresponding conceptualizations, as well as a continuous discourse on the link between theory and methodology. The complexity places high demands on the designs and methodologies from those who are tasked with empirically assessing and fostering improvements (e.g. educational researchers, quality care departments, and educational inspectorates).