This article describes a theory about the ambition of most Inspectorates to realise 'school improvement through inspection'. Literature about a number of direct and indirect interventions, such as reciprocity, communication and feedback is used to build a theoretical model stating the relations between working methods of school inspectors, reactions of schools and resulting effects and side effects. Finally two types of inspections strategies are described that can be used in different types of schools. We expect schools with a low innovation capacity and few external impulses to be helped best by a directive approach in which an inspector clearly points to the strong and weak points of the school, the probable causes of their level of functioning, and potential ways for improvement. The inspector should pressure the school to change by making written agreements on how to change and by asking the school to work out these agreements in an improvement plan. A school with a high innovation capacity and strong external impulses is expected to do better with a more reserved inspection approach. Inspectors only need to provide this school with some insight into their strong and weak points.