I teach Spanish to middle and high school students. I think that if I were to use a blog for my class I would use it as a way for my students and their parents to follow along in my class. I could post weekly outlines with lessons, quiz and test dates etc. This way parents will always know what is coming up and students will know what to expect when they come to class. If a student misses class for whatever reason they can go to the blog and see what they are missing.