The full service extended schools (FSES) initiative in England sought to build the capacity of schools to deploy multiple interventions across a range of child, family, and community contexts in order to improve the lives of children and families, and to enhance the sustainability of the areas where they live. As such, it was part of wider international developments to broaden the role of schools and integrate their work with that of other child and family services. The complexity and indeterminacy of such initiatives present particular challenges to evaluators, and mean that simple input-output approaches to evaluation are inappropriate. This paper reports the use of a theory of change approach to the FSES evaluation. It argues that an approach of this kind is better able to deal with complexity. However, in practice, this approach did not simply replicate standard outcomes evaluation processes in a more context-sensitive way. Rather, it involved fundamental shifts in what counted as valued outcomes, in a focus on potential rather than effectiveness, and in the roles of actors and evaluators. The paper concludes that, as the role of schools widens, educational evaluators will also have to rethink their roles. (Contains 1 figure.)