Edmodo is a private micro-blogging platform built for use by teachers and students for use in the classroom.
Edmodo is not a full social networking application, but more of a messaging tool with more.
Edmodo provides a way for teachers and students to share notes, links, and files. Teachers also have the ability to send, alerts, events, and assignments to students. Edmodo also has a public component built by allowing at the teachers discretion to post any item to a public timeline at the teacher’s discretion. – taken from CrunchBase