Authentic assessment and evaluation allow us to systematically document a child's progress and development. PBL encourages this by doing the following:

It lets the teacher have multiple assessment opportunities.
It allows a child to demonstrate his or her capabilities while working independently.
It shows the child's ability to apply desired skills such as doing research.
It develops the child's ability to work with his or her peers, building teamwork and group skills.
It allows the teacher to learn more about the child as a person.
It helps the teacher communicate in progressive and meaningful ways with the child or a group of children on a range of issues.