By contrast, four-fifths of the difference in behaviour between the general population and children with psychopathic traits seems to lie in the genes.
They then subdivided these children into those with psychopathic traits and those without and asked, in each case, whether an individual's twin showed bad behaviour, psychopathy, or both.
On a practical level it suggests that bad behaviour needs to be handled differently in different children, and will be much harder to eradicate if associated with psychopathic traits (though that does not mean that parents and teachers should not try).