From the Blogger Terms of Sevice:
"You must be at least thirteen (13) years of age to use the Service. Google reserves the right to refuse service to anyone at any time without notice for any reason."
And of course this is entirely silly beings that if you were to follow the directions I gave regarding the settings, your blogs would be as impenetrable as Fort Knox to anyone but you and the students.
Knaus' advice for middle school teachers is to check out Edmodo or to create a private wiki. You can use Google Docs to create a quasi-Wiki which would work just fine. I often use this method when I want the students to summarize a biography or story as a reading check. Sure beats brain-insulting multiple-choice quizzes.