The calling for members of the class to comment on each other’s keyboard performances at Key Stage 3 (not compositions or improvisations) i.e. what was good, what could be improved deserves some thinking about.
There is not a lot pupils can say, or is there?
Responses tend to be predictable and general. It usually boils down to something about accuracy. There may be a danger that responses become formulaic, limited and over time weatherworn.
You might try other strategies.
For example, self-assessment with performers explaining what they are finding difficult, what they are pleased that they have mastered and by demonstrating this to the class.
Or, focus on fingering with pupils justifying their approach to the rest of the class.
Or, you the teacher publicly calling for a pupil to rehearse a phrase with feed back/feed forward coming from you and highlighting improvement. ‘Do it again’ … ‘now again, and this time …’
Or … [late edit]