Once students have signed up on Edmodo, they can use the same username to access many different classes. In order to join another class, they just have to select Join under the Groups heading on the lefthand side of the screen. They will need to enter the access code you were given when you created the class.
Having one username and password has come in handy as middle school students are notoriously forgetful and it keeps things streamlined. Now that I'm encouraging other teachers at my school to get involved with Edmodo, they can easily join classes in other subjects or disciplines.
