How I Use It
I use Wordpress for a teacher blog - http://theglobalclassroomproject.wordpress.com. It has great options for adding many collaborative authors from around the world.
I use wordpress for an education project blog. It works really well; however, it is somewhat complicated for student use, even in secondary school.
Teachers wishing to blog with their students in educational settings (both primary, and secondary) are better off exploring http://edublogs.org, the world's largest education blogging platform.
While this service is NOT free, the technical support is second to none; and the subscription unlocks better themes and features which teachers and students will find useful.