Learning to write is as complex as learning to read or to understand mathematics. It requires a good deal of exposure to exemplars and practice, practice, practice.
Learning to write teaches us how to think. The stronger we become in our abilities to communicate a message in writing, the more we are able to communicate our thoughts, perceptions, and analysis in other forms and in other areas of learning.
The best writing teachers write. (Emails do not count.) They share both their writing and their thinking about process with their students. They understand the complexity of writing because they are experiencing it first-hand.
Writers need authentic audience throughout the writing process (and not simply when the piece has been completed.) It is near impossible to know what others need in terms of clarity and engagement without sharing our work with them.
Copying over work is not publishing.
Writing is best taught by showing students what they know, reinforcing what they are doing well, rather than simply pointing out what is missing.
Writers need choice of topics in order to identify the material and the focus that will serve them best. When writers are provided with choice and a regular writing time, they will write with more engagement, organization, and voice.
Learning to write takes time: time to think, time to experiment, time to revise. Without time, students tend to produce shallow products that show very little improvement (or understanding) from piece to piece.
Writers need to think like writers. If students ask, "How long does it need to be?" they are not identifying themselves as writers.
Writing, when taught well, boosts confidence. The writer's work is received respectfully and seriously; her voice is heard. Once a student has felt a modicum of success in writing, she knows that she can succeed in other areas of her life, too.