The masterclass is that event where the student gets out on stage to be torn apart by an established master in front of an audience. One can liken it to christians being fed to the lions in front of the Roman masses.
In this instance Alfredo Kraus helps a poor tenor, however is compelled to demonstrate:
The single worst operatic masterclasses I have seen are the ones given by Elizabeth Schwarzkopf. This of course is the woman who when asked what were here Desert Island Discs, picked ten of her own recordings. She would pick on students regarding their pronounciation and diction....to the point where not a single note would go by and nothing was actually gleaned from the coaching, except perhaps a hatred for the older generation.
It takes a certain set of brass balls to get up and sing Casta Diva for Maria Callas. For someone who was supposed to be tempermental she is remarkably nice to these kids.