What purpose would a blog serve in an eduational setting?

I am currently in the process of creating my own wikispace with the help of our system technology specialist. I have already posted a link to my blog page on my wikispace. I would like for my students to not only access notes, homework, and worksheets from my wikispace but also my blog page for the purpose of answering and discussing reflection questions once a week. For example, I have already posted a question about opinions concerning evolution. I would use this to not only assess student learning but as a writing tool as well. There are so many students that do not yet know how to correctly write a complete sentence let alone a paragraph. The SAT now has a writing portion and I give essays on all tests so these students really need to know how to express their ideas on paper in a grammatically correct fashion. For the students, the blog page would be a place where they can express themselves and learn how to write about different topics.
What are your thoughts about my ideas concerning blogging as a writing tool in class? Do you have any suggestions that would add to my ideas?