A good example summarizing recent research on Conflict Resolution Education is this pdf of an article by Tricia Jones entitled Conflict Resolution Education: The Field, the Findings, and the Future that appeared in the Conflict Resolution Quarterly in the Fall of 2004.
Another earlier article that provides a number of different vantage points on the issues surrounding peer mediation evaluation is Peer Mediation in Schools: Expectations and Evaluations by William S. Haft & Elaine R. Weiss, appearing in the Harvard Negotiation Law Review, Vol 3, Spring 1998.
While now a bit dated, Marsha Blakeway’s 2002 compiled list of 460 annotated research reports is a goldmine for scholars just getting going on a project. This collection includes information beginning in the early 1980’s on academic research published in dissertations and theses; U.S. Department of Education document references published in ERIC; and unpublished project evaluation reports prepared for school systems or for organizations that funded the project. In some cases, journal articles have been written based on these reports. You can search and view the collection via a special portal hosted by CRInfo.org.
Quick Search: You can use this link to search the ERIC database for recent publications on conflict resolution or peer mediation evaluation and effectiveness research.