Let's say I want to motivate people to contribute to a quantifiable target but I do not want to disclose the value of the target. Example: we need to build a brick wall. Each student can, based on his or her skills, time availability and any other factors, lay an X number of bricks. We know when we set the target how many bricks we need to build the wall. Each student will know how many bricks he or she added to the wall. These will be one time contributions.
Is there any way to provide a feedback to the student on the value of his/her contribution to reaching the target without actually disclosing the target?