Masturbation.

As somebody who teaches sex education in school, the issue of masturbation is sometimes brought up and I always try to answer the questions put to me - indeed, I do not think I have ever shied away from giving a Christian/practical response to anything asked.
This is perhaps a matter of sublimation and there is a need for avoidance of the mental stimuli around which lust is based.
It is extremely difficult to claim that the Bible forbids masturbation.
As a release mechanism, I believe it to be inevitable - research has consistently concluded that all healthy males indulge at various points in their lifetimes, particularly when younger, and most females too.
It is a difficult and sensitive issue and an area which has, I believe - through dogmatic teaching - caused much damage to Christians.
The problem is not the act itself. The difficulty is what accompanies the act. If fantasies are part of the process, are they legitimate?
Where another person is involved in the mind, is that not "Committing adultery in the heart?"
Christianity is based on what is 'in the heart' and so illicit thoughts are sinful.
It is a thin line which Christians need to follow carefully.