As a former teacher, grading makes sense to me. It allows parents to know how their children perform at school.
On the corporate side, grading can let managers know how their new hires performed during a week-long live training event. This gives the managers opportunity to coach some and give kudos to others.
This grading scenario can be set up two ways: 1) attendees are told up front that they will be graded on X, Y, and Z or 2) attendees do not know they are being evaluated so that we can observe how they naturally behave (assuming they will behave in a similar fashion once they return to their home offices). We grade on things like attendance, participation in discussions, body language and attention to the speakers, etc. Much depends on if the person is willing to speak up and give a comment or ask a question (in a class of about 25 people).
Do you grade your attendees at your live training events? Would you let them know beforehand or keep it secret?