It would be easy to use a blog to make connections to home by having students write back with either answers to questions, reflections on a reading/activity/event.  It would also be useful for homework or projects where students can get feedback from the teacher or each other.  Parents could also become more connected to the class/teacher by seeing what the students are blogging to the teacher/class about.

Oh, and that's what makes it a 21st century tool.