Thanks, Brent. The improv team is not graded, as it's "just" an after-school activity. Being a team, there is a selection process and the teacher decides, in a unilateral fashion, who makes the team. In previous years, the student body has voted on team members, making it more of a popularity contest.

You're right in that self-assessment in improv works fairly well. So does peer evaluation because your peers have to deal with what you give them.