Formative assessment is the use of assessment to give the learner and the teacher information about how well something has been learnt so that they can decide what to do next. It normally occurs during a course. Formative assessment can be compared with summative assessment, which evaluates how well something has been learnt in order to give a learner a grade.

Example
The learners have just finished a project on animals, which had as a language aim better understanding of the use of the present simple to describe habits. The learners now prepare gap-fill exercises for each other based on some of their texts. They analyse the results and give each other feedback.

In the classroom
One of the advantages of formative feedback is that peers can do it. Learners can test each other on language they have been learning, with the additional aim of revising the language themselves.

Further links:

https://www.teachingenglish.org.uk/article/assessment-learning

https://www.teachingenglish.org.uk/blogs/cerirhiannon/ceri-jones-assessment-negotiating-exam-formats

https://www.teachingenglish.org.uk/article/tec-2015-interview-geetha-durairajan