Many of the presentations have stressed the importance of the internal logic of prevention programs aimed at improving children's health and development. The logic model explains why a program works. Usually it is based on rigorous research and testing or by careful service design using high-quality local and international evidence.

Mark Greenberg explained the logic underpinning the PATHS curriculum. The argument starts with the way the development of a child's brain is shaped by its environment. The brain re-wires several times during childhood. Faulty wiring has lasting effects, measured in terms of ability to sustain healthy relationships, to learn, behave and be happy.

With regards to emotional self regulation, the brain develops in reasonably predictable ways. At birth, the child expresses what he or she feels and waits for immediate response. By middle childhood the child is managing emotions in response to the complexity of ordinary human relationships. And so the story continues.

All children develop in this way. PATHS attempts to improve the wiring of all children's brains. When the programme is properly implemented, the effect is better emotional regulation for all, and reduced conduct and emotional disorders for the few. It is a classic public health intervention.

Not all prevention models reach so deep. Many focus on reducing the symptoms of disorder, for example reducing the number of crimes committed by young offenders.

It's not essential that programs go deep. But when an intervention changes universal and organic -but maleable - developmental processes such as attachment and emotional regulation, the length and breadth of the impact is likely to be greater than when the focus is on reducing symptoms of disorder.