This paper describes the enlargement of the initial conception of formative assessment with reference to constructivist, sociocultural and situated theories of learning and the concept of co-regulation. It reviews research on student involvement in formative assessment practices (self-assessment, peer assessment, whole-class discussions of criteria and exemplars) in the area of writing, with a focus on primary school classrooms. Student participation in the co-construction of formative assessment is illustrated by qualitative observations from a study of a writing activity carried out in grades 5 and 6. The observations are discussed in relation to findings from other research and implications are presented for teacher professional development and for future studies of formative assessment of writing.