This post claims to provide the world's simplest social media policy.  Whether it is or not is for schools to decide.  However what it does do is provide a checklist that could be the kernel of a procedure document for those schools who decide to embrace social media tools as part of their e-learning armoury and want students to be aware of the potential future consequences of their posts.

The post also contains some other interesting links.

http://theinnovativeeducator.blogspot.com/2011/03/worlds-simplest-social-media-policy.html