This is my favorite blog site for students and has been for years. Whereas it used to be free, there is now a fee required for a teacher account.
I love this site because it a safe way to teach and introduce students to the blogging world.
Students love it as they feel empowered with their own space to share ideas and writing.
The settings can be changed so that the audience is the whole school, just their class, one other class, or other schools across the nation.
It is also supportive of google drive documents and very teacher/student friendly.