The other day, I sat in on a violin master class. I've sat in on a few different master classes for musicians these past couple of years, so if you haven't, here's my basic understanding of what happens.
First, the musician giving the class sits either on stage or in the audience, depending. Then a student performs a piece they've prepared. And then the musician giving the class works on whatever areas or skills they think will be most useful to the student. As they work together, the master also usually talks to the group as a whole, making suggestions about practice skills and strategies and such.
Other students watch and take notes.
The other day, the master violinist worked with two students, each for about 40-45 minutes (including the initial playing of the piece).
In all the master classes I've seen now (maybe four or five), the teachers have been incredibly kind and rigorous at the same time; they've all seemed to take the students' work seriously, and have focused in on really specific areas for further work. And in all the master classes I've seen, the students have been amazingly brave and worked hard to get what the teacher was working on. (I say "brave" because I think it takes real bravery to expose your work and then stand there and absorb critical help, even the kindliest critical help.)
I gather this is a long tradition and happens all over the world in classical music settings (maybe in other music settings, too, I don't know).
Imagine if writers were paid to take that time with students? Not in a class of 20, but one on one for half an hour a week?
Of course, only music students who are pretty serious get chosen for master classes, so it's not everyone. Two of the violin students on campus got to work with this superb violinist, and there are maybe 15 or 20 violinists studying here?
It's fascinating to watch a master class, by the way. For the first student, the master worked on their hand frame for a bit, which seems daunting. (The hand frame is the way you hold your left hand to do fingerings and such while the right hand holds the bow. If you have a good hand frame, you can shift positions and do vibrato and stuff. I'm working on the very basic level myself, but the idea of trying to change my hand frame in a lesson is daunting. It seems like the sort of thing you work with a teacher on for a long time and practice at even longer.)
She also worked on intonation a lot with both students. Intonation on the violin is shockingly hard because if you put your finger down just a tiny bit differently than you should, you're flat or sharp.
And she worked on starting a note with confidence. There aren't any frets on a violin keyboard, so when you put your finger down to start, say on a D above the open string D, you have to know and be confident that your finger placement will be absolutely perfect. And it's one thing for that D, which is played with the third finger in first position; if you've really got your hand frame, then your body knows that placement and you can bow with confidence.
But if you switch to, say, fourth position and play a higher note, then it's a lot harder, I gather (I'm not there yet). You REALLY have to have practiced it so much that your hand frame in fourth position is as confident as in first position, and that's a whole lot of practice.
(If you look at my violin, or the violins of lots of "younger" players, we have tape across at several places to help us know where to put our fingers initially. But once students develop a really good ear and hand frame, the tapes go away. I'm not there yet. At any rate, no one seems to use tapes for above first position.)