The term ‘assessment’ refers to all those activities undertaken by teachers, and by their students in assessing themselves, which provide information to be used as feedback to modify the teaching and learning activities in which they are engaged. Such assessment becomes ‘formative assessment’ when the evidence is actually used to adapt the teaching work to meet the needs.
The definitive paper of formative assessment was ‘Inside the Black Box, Raising standards through classroom assessment’ by Paul Black and Dylan William