In 2008, the American Bar Association published Final Report – Task Force on Improving Mediation Quality. Interestingly, the task force '[a]fter determining that a national credentialing program was not feasible for the current [US] mediation market place' (compare Australia!), retreated to the less controversial and arguably less difficult topic of 'factors that define high quality mediation practice.' (ABA p2).
Available at: http://works.bepress.com/john_wade/65/