Formative assessments are assessments that occur during lessons, while Summative Assessments are those that take place once the lessons/units/part of the curriculum have reached an end. Summative Assessments are highly important, as they provide evaluators with arrays of useful information about the taught.
why summative assessment?
'Summative' assessments are set to enable teachers evaluate, and assign a mark to their students' learning at a particular point in time. The mark assigned contributes to the final outcome of the students' learning degree.
The most important thing when completing any form of assessment or examination is to establish what the goalposts are, by looking at the marking criteria for the assessment.