Edmodo allows students to interact with each other as they would with their friends and family on Facebook and Twitter. You just create a free account and the magic happens. Teachers can create groups where students can message them and get class materials.
It also works the other way around. Teachers can find useful items to enhance their classes and also interact with other teachers on the network.
To sign up is free, all you need is a group code from your teacher and you will be on your way to a new form of education.