Short for Web Logging, blogging has been a popular way of communicating only recently "replaced" by Twitter and Facebook updates.
One site that has a lot of free (and we like free!) features for up to 50 students with minimal attachment size (extra data Costs More!) is kidblog.org.
Either create student accounts with pre-defined passwords, OR get the secret code that will allow ALL your students to register for your blog site. (Don't do both, or you'll get two accounts, one you created, and one the student created with the secret code)
The teacher controls the posts by the approval method and can suggest to the student that the post be edited or otherwise modified.
Lots of safety features, and accessible on the iPad as well as the browser on the laptop/desktop, so this is a great resource all around.