Most health problems are getting better. But one that’s visible in every classroom in the land is getting worse. A study last year in the British Medical Journal found that the proportion of children who are overweight had risen in 10 years from 14.7 per cent to 23.6 per cent - and that’s just among the under-fours. The incidence of obesity had risen to 9.2 per cent, the Liverpool University researchers found.

Obesity in children is accelerating across the western world, with all the attendant dangers, including heart disease, diabetes, poor vision, kidney damage, bad circulation and, according to recent German research, asthma.

If the dangers are increasingly well charted, the solution is not. Year 6 pupil Daniel Smith was a hungry baby, and bigger than his classmates even at three. “You can see it in the nursery photos,” says his mother, Jan Smith. “He doesn’t overeat as such, but he likes to eat the wrong foods.”

As Daniel grew older, he turned to comfort eating and secret snacking, hiding chocolate wrappers and crisp packets in his bedroom.

Daniel, like many fat children, was ostracised by his peers. By Year 5, he was focusing his anxieties about the social situation on his maths performance. “We tried to show him that his maths was level with everyone else’s, but he couldn’t see it,” says Marguerite Heath, head of the 630-pupil Dover Road community primary school in Northfleet, Kent. “His main problem is at playtime, and has been all along, because the boys especially tend to play running-about games, and he can’t keep up. He has had quite a lonely time.”

“Our home life was a wreck,” says Jan Smith. “We had to try to get him to school in the morning, kicking and screaming. He didn’t sleep at night and, if he did, he’d be tossing and turning.” In Year 5, Daniel had three months off school, sanctioned by the GP, and was prescribed tranquillisers. When a local teenage boy hanged himself, he told his parents that he too had suicidal impulses.

Daniel Smith was assigned a teaching assistant to help him gradually re-enter school. He was met every morning at the gate by the family welfare worker, who provided moral support. “Children can’t learn unless their emotional needs are met,” says Ms Heath. “It was a special need, at that time.” Staff at Northfleet - which numbers several obese children among its pupils, and more with the gross motor deficiencies that also result from inactivity - are aware of the issues for him and many others. They have employed a PE instructor who does “pop mobility” dance sessions to music, a form of exercise the children enjoy. The school puts on an “exercise club” for half-an-hour each day aimed at those with weight andor co-ordination problems; 25 children attend.

But excess weight is an intractable difficulty. Since last autumn, Daniel has benefited from a pioneering programme run by staff at University College, London. Modelled on successful work in the United States, the UCL programme is a family-based, behavioural programme that helps children absorb and follow a simple set of dietary guidelines called the “traffic lights” diet, in which foods are divided into green, amber and red categories, according to their calorific properties. “It’s important to have a simple model kids can follow,” says Jane Wardle, professor of clinical psychology at UCL, who leads the pilot project which is backed by the charity Weight Concern.

Children are given pedometers to measure how much distance they cover - “they’re fun and entertaining,” says Professor Wardle - and set goals for increased activity. Progress is assiduously monitored, and progress in meeting the goals - changes in behaviour rather than specific weight-loss targets - is rewarded with non-food treats such as toys, magazines or the chance to watch television programmes. Children and their parents talk over in groups “the general misery and nastiness of life if you don’t square up to what people think of as ideal”, says Professor Wardle.

Many report teasing, not only from peers, but from teachers and health professionals. But the biggest boost for all concerned is helping children and families to gain the upper hand over something that’s been out of control. “That greatly increases self-esteem.” All the children taking part have improved their heightweight ratio, she says, some of them substantially.

Daniel was accepted on to the programme after his mother answered a newspaper advertisement asking: “Do you have a child who’s overweight and do you want to do something about it?” His progress has been filmed by the BBC and is the subject of a sensitive documentary to be screened on BBC1 next week, featuring a range of approaches in Britain and in the US.

Daniel hasn’t lost weight. But he’s grown in confidence, taken up hand bell-ringing and discovered a propensity for shot putt. With help, he has learned to deal with name-calling. “I don’t think about doing myself in any more,” he says cheerfully.

Contrary to stereotypes, says Professor Wardle, most overweight children and adults will not “have been visibly gluttonous”; just a small amount of regular excess will lead to inexorable weight gain. “Society as a whole has an important task to make our environment less ‘obesogenic’. We all have a propensity to overeat, and we all now live in an environment where we’re all encouraged to do so, at every turn.”

Too Fat Too Young, BBC1, Tuesday, July 9, 10.35pmwww.weightconcern.com