Teachers seeking online communication and collaboration opportunities with students and other educators have another free resource at their disposal: Edmodo, an education-based social networking site.
The social learning network for teachers, students, schools, and districts offers free classroom communication for teachers, students, and administrators on a secure social network. Professional development for teachers is another component.
Teachers and students can post classroom materials, share links and videos, and access homework, grades, and school notices within Edmodo, which stores and shares all forms of digital content—including blogs, links, pictures, video, documents, and presentations.
Write-up via eSchool News, which is how I found this. I would have directed you there, but they seem to think an effective business model is this many ads ::opens arms real wide::, and this much content ::pinches two fingers together::.