An ELT Glossary : Formative and Summative Assessment
Assessment of learners may be carried out for either of two purposes :
a) Formative assessment is used to improve the quality of future learning - ie to help the teacher and learners decide how successful their learning has been up to that point, what needs recycling and consolidation before they can move on, whether different learning strategies need to be introduced and used etc etc. Examples of tests with a formative purpose are diagnostic tests and progress tests.
b) Summative assessment, on the other hand, evaluates the success of past learning in terms of pass/fail or various forms of grades. They show to what extent the learner has or hasn't achieved the standards required by the programme. Examples of summative tests include achievement tests and proficiency tests.