What is the purpose of assessment in schools?

This posting is for Purpos/ed - What is the purpose of assessment in 500 words....

I would like the answer to be "to improve student learning". But there is not one purpose of assessment but very many.

Assessment is used nationally to categorise learners so that they can have access to further learning,  or to rate the quality of the learner's institution. At this level it is definitely summative and the process is complex and not very transparent, so it is difficult to judge whether either of these two purposes are being carried out effectively.

Assessment is used by parents to try to judge both their child and the school. Parents are often more interested in comparing their child with others of the same age range than the individual progress that the child has made. It is summative, can be formative, and should be ipsative.

Assessment is used by teachers to gauge individual and class prior learning and eventual learning. It should be diagnostic, ipsative and formative. It will also be summative at appropriate times.

Assessment is used by schools to gauge how learners are learning and possibly how teachers are teaching. It is summative on the whole.

Assessment is used by learners to gauge their self-worth. Therefore it matters and will affect the learner’s attitude towards subsequent learning. It is invariably summative even though teachers believe the assessment information to be diagnostic, ipsative and formative.