Pupils should be weighed and measured regularly from pre-school onwards to identify those in danger of becoming obese, according to a government adviser.
Tam Fry, chairman of the Child-Growth Foundation, said that schools and nurseries have a crucial role to play in tackling obesity.
They are already weighed and measured in reception and Year 6 to calculate their body mass index. Those with a high BMI are labelled "overweight" or "obese". But Mr Fry believes this is not enough.
"We already measure schoolchildren," he told a conference on tackling childhood obesity in London this week.
"But to address the epidemic problem of childhood obesity, I hope this will be extended to pre-school as well. The sooner we start putting that into progress, the better statistics we will have."
There was support for his suggestion from Ashley Adamson, senior lecturer in public health nutrition at Newcastle University.
"The joy of schools is that we have a captive audience there," she said. "If you can influence children, they can go back to their parents and use pester power. Children can be the change agents in their families."
Will Cavendish, director of health and wellbeing at the Department of Health, agreed that such measures would help "reverse the rising tide of obesity".
"Findings show that one in four children are overweight or obese at reception," he said. "We need to make childhood obesity a real priority in every single part of this country.
"Childhood obesity doesn't suddenly pop up at age four or five. The two- year-old stage is a time of rapid growth and change.
"We want to get a situation where every child is a healthy weight."
Harry Rutter, director of the National Obesity Observatory, believes that ongoing measurements throughout childhood could provide additional insight into pupils' development.
"There seems to be a relation between obesity and school record," he said. "So it's also about attainment. Measurement has to be there to support action."
But Susan Ringwood, chief executive of Beat, the eating disorder charity, argues that any measuring in schools must be carefully handled to avoid imbuing children with a fear of food.
"Anything that heightens people's awareness that there are good and bad foods can be unhealthy," she said. "Everyone has an emotional relationship with food, but for some people that relationship becomes unhealthy, even toxic. When people use food to control and suppress emotions, that's where the problems start."
She suggested that schools make use of eating-disorder expertise when discussing food with pupils.
"Unless you're able to engage with people's emotional relationship to food, you're not going to do anything about the problem," she said. "We need to look at emotional resilience. That's how people with serious emotional illnesses make changes in their lives."
What a load of BMI, page 31
A growing problem
In 1995, the World Health Organisation lowered its definition of "overweight" and Hollywood actor Russell Crowe was among the millions designated obese overnight. Since then, the Government has been fighting a national "obesity epidemic".
In 2005, the National Child Measuring Programme was introduced in schools. This weighs and measures all reception and Year 6 pupils to spot trends and identify any who are at risk of becoming overweight.
In 2007, the Government pledged that all pupils would be able to do five hours of sport each week, including two hours within the school curriculum.
And this month it reiterated its Pounds 56.3 million pledge to install cooking facilities in schools and to train staff to teach the subject. This precedes compulsory cookery lessons from 2011.
Most schools now preach a healthy eating, healthy living message, and 97 per cent have signed up to the Government's Healthy Schools programme.