Like any tool, I think using blogs has to be built upon. My main goal in the beginning is to have students pay close attention to grammar! Sometimes I feel like a broken record... "Capitalize the beginning of a sentence! If you capitalize your name, why wouldn't you capitalize your friend's name? You just wrote a paragraph and have no punctuation!" I believe it would be beneficial for students to see what and how their fellow classmates write. Most of the time they know that I am the only one who is going to see their writing. If they know their friends will see their responses, maybe they will spend more time with capitalization and punctuation. And maybe, just maybe, some of them will try and write more than a couple of sentences!
After tackling grammar, I will start out having students respond to stories I read aloud or stories we read together. Students can discuss their favorite characters, parts in the story, or even change the ending to a story. Since I teach reading, language, math, science, and social studies, students could also create a hypothesis on experiments or become a character in history. Eventually, I hope that we can work our way up to more critical thinking questions but I have to begin somewhere.