One of the advantages to having students do their work in Google docs is the “Email Collaborators” option under the file menu.

If students share their documents with you then when you go to grade their documents you are able to “Email collaborators” and give the student feedback.  They know you graded the document, you do not have to look up their email address, and you can give them specific feedback on how to improve.

Another suggestion would be to have students not only share their documents with the teacher, but also with their parents.  This way parents can see the work the student is doing and when the teacher emails collaborators the parent will receive the feedback as well.