Evaluation for the purpose of improvement is said to be formative, and focuses on producing feedback so that teachers and students can improve their performance. Evaluation for the purpose of accountability is said to be summative. It focuses on overall judgments of performance, and is directed at an external audience. In practical terms, the same assessment methods and instruments can be used for both formative and summative evaluation. Feedback is specific evidence about how a person performed with respect to a standard for performance.
Feedback is critical to better performance.
Without it, a student has no information about what to do in order to improve or develop. But feedback is simply information about how one did compared to a standard. In some activities feedback is a byproduct of the performance. For example, musicians receive ongoing feedback as they play a piece. Ostensibly, if they know what a piece should sound like they can compare what they produced against the ideal standard.