Non-profit organisations are under increasing pressure to demonstrate their social impact. This paper examines the experience and behaviour of non-profit organisations in the UK in relation to a demand for impact evaluations. It shows that organisations both accept and resist control, and use evaluations for promotional purposes. External resource providers request organisations to present evidence on how resources are used and what organisations have achieved. However, non-profit organisations can also proactively use social impact measurement as a way of exerting control over their environment through using their discretion in deciding what to measure, how to measure and what to report. The analysis uses a combination of the concepts acceptance, rejection, compliance and strategic decoupling to distinguish different organisational responses to external demands for impact evaluation.