To enable teachers to become "transformative intellectuals" (Huckle, 1996), a critical form of educational inquiry that enables them to investigate their practice, is required (Robottom, 1987). Such an approach was used in developing assessment resources and materials "with" teachers, not "for" teachers. The important thing is to help teachers help themselves by sharing with them ways of developing the tools and skills of assessment. This paper describes how I engaged teachers in a process of mobilising "assessment capital" through a participatory action research approach. This was used for the development of assessment resources and materials, in order to foster improved student engagement and learning. A case study of one school is presented in this paper. This school had multiage classes. The case study highlights the potential role of teachers as transformative intellectuals in schools. (Contains 1 table and 1 figure.)