I exchanged e-mails with poet Adam Penna, who edits Best Poem, about the difficulties of teaching writing. What he had to say makes such good sense that I'm preserving it here:
I've found that the best and only way to teach writing is to begin to redefine for my students what it means to write. I spend a lot of time defining terms. Essay = to try; revision = to re-see; research = to look again. For me writing and the teaching of writing are opportunities to listen to oneself talk. Usually, the consequence, for those who are willing to listen, is the realization that they haven't been paying close attention to what they say. Once they begin paying attention inevitably many of the mechanical irregularities improve. And paying is the important term here, considering that it implies a metaphor most people understand. That is, care = time and time = money. Further, I steal an equation my former mentor taught me, which is care = talent. Or, rather, talent is a way of caring, as he put it.