Yes, I am an advocate of student blogging. Yes, I helped create the #comments4kids meme on Twitter and made the Comments4Kids blog. Yes, I have presented both online and face to face on the value of blogging in the classroom. Yes, I know that blogging isn't the answer to your students' writing needs.
While reading some blog posts by college students today and mixing that in with my thoughts on what I am going to present next week at a technology conference session on blogging I had a conversation with Nancy Van Erp that helped me clarify my thoughts.
To become a better writer, practice is required. Along with the practice there needs to be specific feedback that addresses issues with the writing. It simply isn't enough to praise the fact that the students wrote something, or that addresses the content of the writing without touching style or context. Let's face it, specific writing feedback on a blog post is very difficult for the writer to take. Imagine having your shortcomings exposed to the world!
I am not suggesting there is no value in posting work that isn't polished. If that were the case most bloggers would never post a thing. What I am saying is that for teaching writing, blogging isn't the best choice. Your students will learn much more and be less likely personalize their mistakes if you have those conversations face to face.
Where blogging shines is through the ideas shared and the conversations created by posting online. If that isn't the goal of your writing assignment, perhaps you need to rethink the medium you have chosen for your students to use.