This paper will report upon a complex formative evaluation of a comprehensive Year 9 innovation in a large independent girls' school. The paper will contextualise the innovation in terms of continuous school reform in what may be identified as an 'activist' school. Its main purpose will be to report upon the forms of evidence that are being assembled to inform the evaluation. A wide range of both quantitative and qualitative procedures have been adopted and their complementarity is considered within a discussion regarding the use of mixed methods in a single case. The paper will consider some of the practical issues relevant to the process along the lines of barriers and facilitators to good, effective mixed methods research. It will embody practitioner researcher and academic researcher perspectives.