Parents who exert firm but fair control over adolescents are much more likely to steer them away from drugs, delinquency and crime, Scottish researchers have found.
Youngsters whose parents are overbearing, inconsistent or lax are at far greater risk of becoming problem teenagers, the long-term study of criminaloffending shows.
Closely supervised adolescents who are allowed some autonomy not only stay out of trouble but have fewer rows and less conflict at home.
Researchers who are tracking 4300 young people in Edinburgh over 20 years found high levels of delinquency, drug-taking and smoking among children of 12 and 13.
More than half of the youngsters admitted to two or more delinquent acts, such as shoplifting, fighting, vandalism or theft, in the previous year.
Parenting style was a main influence on whether young people engaged in criminal or delinquent behaviour, said David Smith, who is leading the study at Edinburgh University.
The most successful parents are those who are prepared to negotiate and have clear ground rules, such as knowing where their children are, who they are with and what time they are to come home.
"Parents who trust their children but are firm and active in supervising them have a lower degree of conflict than parents who try to lay down the law," Professor Smith said.
The least successful parents are those who are autocratic, those who make arbitrary and intermittent attempts to control their children or make threats which are not carried out.
"Inconsistent parenting leads the child to conclude that behaving well doesn't get results.
"Parents who are most in conflict with their children are those who supervise them least," Professor Smith said.
The Edinburgh research, which aims to find out why some young people become deeply involved in offending while others do not, is the biggest longitudinal study of its kind in Britain.
The first findings suggest that cannabis is commonly tried by adolescents, and use rises substantially as the teenagers grow older. Smoking rates also rise rapidly, particularly among girls.
At the age of 12, 5 per cent of all pupils had smoked during the previous year, but that rose to 23 per cent at the age of 13 when 5 per cent were smoking every day.
Nearly 10 per cent of girls at 13 smoked once a week or more, compared with 7.5 per cent of boys.
Delinquency also increased more rapidly among girls than boys between the ages of 12 and 13.
