EmyB, that is a really good question.
The American Psychological Association, which is pretty much the governing body of Psychologists, recommends the following based on this research;
"The intervention program is built on four key principles. These principles involve creating a school - and ideally, also a home - environment characterized by: (1) warmth, positive interest, and involvement from adults; (2) firm limits on unacceptable behavior; (3) consistent application of non-punitive, non-physical sanctions for unacceptable behavior and violation of rules, and, (4), adults who act as authorities and positive role models. The program works both at the school, the classroom and the individual levels, and important goals are to change the "opportunity and reward structures" for bullying behavior, resulting in fewer opportunities and rewards for bullying".
taken from http://www.apa.org/research/action/bullying.aspx
But I am having a look through my notes as we speak, and will get back to you if I spot some other info that could be helpful.
So good to hear so many parents such as yourself are trying to tackle this issue.