Nobel prize-winning economist James Heckman raves about a 1980s programme for growth-stunted toddlers in Jamaica. Trained health aides visited mothers living in poverty for an hour a week and coached them in how to stimulate their children through play.

The intervention, run by British researcher Sally Grantham-McGregor, was simple but it changed those toddlers’ lives. Monitoring into adulthood shows they have gone on to do better at school, earn more money and enjoy better psychosocial skills than their origins would have predicted. They were also less prone to committing crime.

In short, training the parents while their children were still small seemed to be a magic bullet for a wide range of social problems. “Programmes like this are cheap, effective and don’t require large infrastructure,” says Prof Heckman, who, at 73, runs the Center for the Economics of Human Development at the University of Chicago in his hometown.