Probably should not be posting having not seen the puzzle; however....
I would have thought "she's a class act" would by SCHOOLsomething and was wondering about schoolmate but I am not totally convinced. I assume the M and T are correct?
Final thought (ps) extremely short - s and t, giving psst for the intervention.
Band is the Who with a for answer, giving whoa.
Not the two most common words!