Bardiac lays it out.
My favorite paragraph:
I can't teach a student to be a brilliant writer in one semester any more than you can teach your best incoming tuba student everything s/he needs to learn about playing the tuba in one semester. A really promising high school student has probably learned a fair bit about writing by the time s/he gets to college, and I can (one hopes) help him/her improve. A less promising incoming student should also improve. It's worth noting that I'm teaching all of these students in a class of 20, so I don't have the one on one intensity of your trombone studio private lesson.
Although many other excellent points get made as well.
1 hour ago