Google's Blogger service makes it easy for teachers to quickly create a classroom blog. If your school uses Google Apps for Education you can make Blogger one of the services available within your domain thereby making it even easier to post on Blogger. One shortcoming of Blogger is that there isn't an obvious way for you to moderate students' posts before they go live on a group blog. The solution is to use the "post via email" setting in Blogger. In the video embedded below I demonstrate how to use this setting and explain a bit more about it.
Click here to find screenshots of the process outlined in the video.