From Google Docs:
Teach Collaborative Revision with Google Docs
Revision is a critical piece of the writing process—and of your classroom curriculum. Now, Google Docs has partnered with Weekly Reader’s Writing for Teens magazine to help you teach it in a meaningful and practical way.
Focusing on group work, peer editing and revision skills, Google For Educators offers a tutorial, several articles, and PDFs on using the collaborative features of Google Docs in the writing process.
A link not to miss is The National Council of Teachers of English powerful statement of Professional Knowledge about the Teaching of Writing. These guidelines can inform teaching practice using technology – blogging, wiki use, or collaborative documents by focusing on the writing process, not the tool.