Musicians are used to working in isolation (all that practising alone), so some pianists feel very shy about talking in front of the class. Be careful about assuming that pianists will be delighted to comment from the piano. “Now, we’re all going to gather round the piano while Miss X plays that music again, and this time we’re going to listen carefully. What’s the name of that lovely piece, Miss X?” can be very intimidating unless the pianist feels confident with the students.
If you want to do something like this, give the pianist adequate warning – a lot of the discomfort is due to feeling unprepared when the teacher says something like “And now we’re going to listen while Miss X plays us two lovely, contrasting pieces of music”.
