Twiducate is a new site that I just found out about from Larry Ferlazzo. This is an excellent to provide social networking skills in a safe school environment. It is very similar to Moodle in that respect.
What makes Twiducate so great is that everything is being monitored in a controlled environment that is password protected. Teachers can use it to post assignment, share ideas, and even collaborate w/ parents.
I highly recommend checking out Twiducate by clicking here.