Below, find a bibliography of excellent professional reading on this topic.
Beach, Richard. Teaching Writing Using Blogs, Wikis, and Other Digital Tools. Norwood, Mass: Christopher-Gordon Publishers, 2009.
Herrington, Anne, Kevin Hodgson, and Charles Moran. Teaching the New Writing: Technology, Change, and Assessment in the 21st-Century Classroom. New York: Teachers College Press, 2009.
Excerpt about Collaborative Digital Writing from Ch. 3: