I use WordPressMu on shared server space with my fifth grade. It can easily be configured to keep the blogs private. In fact using the More Privacy plugin gives you 5 levels of access from wide open to just people subscribed to an individual blog.
With WPMU you can use fake emails as you can set the password as an admin. Yes, they each had their own usernames and passwords. I was able to set up blogs for students, classes, and teachers all with different configurations in terms of access and ability to post with or without moderation.
You can make one blog private and the other open (or shades in between). It is quite configurable. It can be a bit more difficult than other software to install unless you keep it simple.
A regular "adult" blog is easy enough for them to use and they get to use a real tool rather than something simplified for kids. I think that is important.
I also found edmodo, which may be an option. I can't really speak to its functionality but they do a decent job of explaining things on their blog. I do know that you can keep it private. I am awaiting approval from my district to use it, but it's something else for you to look into.
If your district is committed to student/teacher blogs, they need to invest in Mac OS X Server. It costs about $6,000 but it's well worth the money. We have 3TB of space, lots of security, host our own data, manage all accounts ourself, and total control over everyones permissions. Not to mention it has some other great features as well.
If they are not willing to make the commitment, go with edublogs.com.
As much of a Mac fan as I am, I have run WPMU off a $10/mo Linux shared server account allowing us to host our own data, manage accounts, and control permissions. Plus we had several other apps running like Joomla, Moodle, and MediaWiki.
I don't think it's just a choice of a Mac server or Edublogs.
If you want to run it on your own server, you really don't need much of a machine to run a LAMP environment unless demands are particularly great due to size of district.
I never said it was just a choice between those two items. I'm not real knowledgeable about LInux so I can't speak for those programs. I do know that a lot of our staff members have really enjoyed the blogs/wikis on Mac OS X server and it has been incredibly easy for our tech staff to manage as well.
You don't really need to buy an xserve. You can run the Server software on an old G4 or G5 and probably be just fine for only wanting to do blogs. That wouldn't cost you anywhere near $6,000.
Thanks! I love the idea of being able to delete comments. Have you ever thought about having the posts "held" until the facilitator (teacher) views and decides if the post should be put on the web? Or is this an option?
We do net explicitly state that Edmodo is for individuals 13 or older? We are not a public site, and do not store personally identifiable information about students. Not sure where you read that. If you had read that somewhere, it's an error.