A similar idea in a group setting is the fist-to-five idea suggested by Marquet. On the count of three, everyone shows either a closed hand (lowest score) or anything up to five fingers (highest score) and then you can discuss both what would get people to a 5, but it's usually also very instructive to dig into why different people make different assessments. (As long as you don't do it in an adversarial way, of course.)