Earlier this week I received an email from an employee of Posterous telling me that a couple of my blog posts had led to them receiving a wave of emails from teachers looking for more information about group blogging. In response to taht wave, Posterous created a how-to video that demonstrates the steps necessary to create your own group blog using Posterous. The video includes how to make your Posterous group site private.
Watch the video below.
You'll notice the video includes registering a custom domain for a fee. You can do that if you want, but it's not necessary for using Posterous.
Applications for Education
As the video above demonstrates, Posterous could be a good option for creating a private group blog. If you're looking for your students to each create their own blogs, Posterous makes it easy for them to do that too.
Here are some related items that may be of interest to you:
How Students Can Blog Without an Email Address
Posterous - A Simple Way for Students to Blog
Free 33 Page Guide - Google for Teachers