This paper explores school development processes in four schools in challenging circumstances. These schools were selected from a sample of schools in a longitudinal mixed-method study over a five-year period of around 100 schools using a typology of different models of change over time. The paper presents first selected findings from the overall study, the typology of different models of change. Then it focuses on identifying organisational changes in the four schools. Based on the analysis, the paper discusses interventions and conditions for school improvement and challenges with respect to applying the intended impact logic underlying prevailing school turnaround approaches. It focuses on the complexity of context and culture. Contingency theory is applied to develop a theory of school turnaround.