In classes, getting students to produce shorts has the advantage of compare and contrast. This is obviously less easy with novels on often vastly different subjects. The discipline of the short story, the need to say as much as possible in a few words as possible is an excellent teacher. The ability to paint briefly is not wasted but makes the eventual novelist a better one. John Gardner was very keen to emphasise the usefulness of small focussed exercises in which the student could concentrate on selected areas of his art.
Teachers can shape and point far easier when the target is an exercise or short story.
Less Waste, More Material A wasted novel is for most beginners a wasted year. A wasted short story is typically a few days or a week. Though it is true that theoretically a student could write 52 consecutive wasted short stories, experience tells us otherwise, since, after every story, finite, complete, the student has usually learned something. In the case of the novel the student does not learn much until he has completed his long and arduous task and submits. Nothing Wasted Novels are rarely honed down to short stories.