The impending closure of Posterous Spaces has me back to recommending Blogger for quickly creating group blogs. One of the aspects of Blogger that makes it easy for students and teachers to write new blog posts is to post via email. If you can write an email, you can post to a Blogger blog. The screenshots below show you how to enable posting via email. (click the images to view them in full size)
Step 1: After signing into your Blogger account select settings from the drop-down menu next to the name of your blog.
Step 2: Select "mobile and email" in the settings menu.
Step 3: Specify the secret email address to which posts will be sent. Select "save as draft" if you want to moderate posts before they appear on your blog.