This question came up recently in the writing workshop I participate in, and here is what Francine Prose answers in her recent book Reading Like A Writer:
"Can Creative Writing Be Taught?
"What confuses me is not the sensibleness of the question but the fact that it’s being asked of a writer who has taught writing, on and off, for almost twenty years. What would it say about me, my students, and the hours we’d spent in the classroom if I said that any attempt to teach the writing of fiction was a complete waste of time? Probably, I should just go ahead and admit that I’ve been committing criminal fraud.
"Instead I answer by recalling my own most valuable experience, not as a teacher but as a student in one of the few fiction workshops I took.
(She praises the editing help of the teacher, and the help she got by being ‘listened’ to, by the class, while she was reading her own work in those 'few' workshops she herself took.)
"That’s the experience I describe, the answer I give people who ask about teaching creative writing: A workshop can be useful. A good teacher can show you how to edit your work. The right class can form the basis of a community that will help and sustain you. But that class, as helpful as it was, was not where I learned to write.
"Like most, maybe all, writers, I learned to write by writing and, by example, from books. Long before the idea of a writer’s conference was a glimmer in anyone’s eye, writers learned by reading the work of their predecessors. They studied meter with Ovid, plot construction with Homer, comedy with Aristophanes; they honed their prose style by absorbing the lucid sentences of Montaigne and Samuel Johnson. And who could have asked for better teachers: generous, uncritical, blessed with wisdom and genius, as endlessly forgiving as only the dead can be?
"The truth is this sort of education more often involves a kind of osmosis. In the ongoing process of becoming a writer, I read and re-read the authors I most loved. I read for pleasure, first, but also more analytically, conscious of style, of diction, of how sentences were formed and information was being conveyed, how the writer was structuring a plot, creating characters, employing detail and dialogue.
"This book is intended partly as a response to that unavoidable question about how writers learn to do something that cannot be taught. What writers know is that, ultimately, we learn to write by practice, hard work, by repeated trial and error, success and failure, and from the books we admire. And so the book that follows represents an effort to recall my own education as a novelist and to help the passionate reader and would-be writer understand how a writer reads."