I recently did a singing course which was delivered as a weekly 'master class', so we each got to hear each other's critique - which sounds a bit like what you're proposing, I think?

One of the things the teacher was really good at was identifying what each person needed. So some people were coached mostly around singing technique, some around confidence (or at least appearing confident), some around storytelling, some around musicality... It was really helpful to have a chance to go back and do a bit again as well, straight away, to put the tips into practice before we forgot them.

In terms of helping people to develop self-critical vocabulary, partly you do that by modelling precise and constructive criticism. We also had a few times when we were asked to comment on each other's performances - obviously when we'd reached a stage where the teacher knew we wouldn't destroy each other's confidence!

I agree with Smedley above, with the (perhaps obvious) addition that the positive comments need to be genuine - false praise can be really obvious and more off-putting than criticism. At the risk of being contentious, I think 'enthusiasm' is a fairly luke-warm complement and I'd be gutted if that was the best a tutor could come up with to describe my performance!