Evidence from the health field

International research on peer involvement in health documents the supportive effect peer work has on changing people’s attitudes, risk behaviour, levels of information, negotiation skills and self-esteem.  An example is Medley et al. (2009) who reviewed 30 studies on peer programmes in the period 1990-2006).
http://www.ncbi.nlm.nih.gov/pubmed/19519235

Research also focuses on the impact on peers themselves.  Involvement in programmes is reported to be largely a positive experience, resulting in increased knowledge, positive changes in attitudes and improved health and wellbeing.
The peer advocates of certain health interventions are reported to be effective in supporting in people in making health choices, such as taking HIV prevention measures.  One example is a study from Fogarty and al. (2001) on condom and contraceptive measures. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1913678/pdf/pubhealthrep00206-0105.pdf )

Peer educators also tend to report greater confidence, maturity and independence and have developed interpersonal and presentation skills (for example, Strange et al., 2002b)
http://her.oxfordjournals.org/content/17/3/327.full.pdf

A Peer Support Forum briefing paper makes interesting reading for further reading on evidence on peer work in sex education. http://peersupport.ukobservatory.com/psia/PDF/ps%20in%20sex%20and%20relationships.pdf