The Massachusetts Attorney General's Office, in collaboration with local community mediation programs, funded the Student Conflict Resolution Experts program (SCORE) from 1989 to 2009.  Attached, find two solid resources for peer mediation:

The SCORE Quick Reference Guide to Peer Mediation for Students; and

The SCORE Coordinators' Manual.

The Quick Reference Guide contains some excellent points about how to run a mediation.

Further, check out the Coordinators' Manual for some great examples of how to start/run a peer mediation program, sample forms and lesson plans!