Bloggin is forbidden is one of American school. It's not that you can't blog when you're at school. No. You can't blog at all.
The principal said it's "an open invitation to predators". The thing is that the new rules are not about posting at all: they're against posting about the school. It means that the children are not allowed to express their opinions about it. It looks that that was the reason of the ban, nothing more.
As I have written many times before, such bans don't work. You can post what you want when you're careful. Using anonymization software it's rather safe. Just another example of absurd regulations.