Here is some preliminary information for you and or your classes when introducing them to the concept of blogging.
WIKIPEDIA: including lots of links to other related issues such as free speech, community blogging and the rise in the popularity of blogs in recent years.
Here is a fun introductory video that explains the concept of blogging in the context of news media, but you can apply this to anything, really…
Also, it may be helpful for you to have a look at some other education blogs. WP always has a showcase of killer blogs, including ones just for higher education here.