In my social issues class, I'm having students do a big group presentation, where I assign 50% of the grade and their classmates assign the other 50%. We use the same grading criteria (interesting/good information/visuals/handout). It's the first time I've done presentations this way and the results so far have been quite interesting.
The students assign grades an average of 4 points lower (out of 35). I think it might have something (A LOT!) to do with only 30% of the class being able to get "A's." Or, they might have higher expectations. One thing I have noticed is that they seem to like the presentations that I thought weren't great, and not be so impressed with ones that I liked. For example, one group had an excellent presentation, but they had some technical issues with their Powerpoint. I would never grade a group lower due to technical difficulties, but most of the class did, and commented on it being an issue. And, the students seem to be a lot more forgiving than I am about students reading their presentations (even though I told everyone it was a big no-no). Maybe they feel some empathy!
An interesting experiment and one that I'd probably do again in the future. It definitely prevents people from sleeping!