Scotland's "Assessment is for Learning" initiative (AifL) seeks to introduce a co-ordinated national system for assessment in schools. Formative assessment is a major plank in this. The initiative has moved beyond its pilot phase and it is intended that it will be adopted by all Scottish schools by 2007. This article draws upon the case-study of a primary school that has adopted a whole-school approach to enacting the formative assessment principles of AifL since 2004. It utilizes Margaret Archer's social theory to analyse and explain the processes of change that have underpinned the development of formative assessment in the school. The article argues that meaningful change in schools can be stimulated by encouraging socio-cultural interaction among practitioners, via the impetus provided by a central initiative combined with the creation of spaces for dialogue and the extension of professional trust and autonomy.