Child obesity expert Laurel Edmunds is calling for a re-think of PE lessons to make exercise more appealing to children.
Dr Edmunds, who is backing the TES Get Active campaign, said far too many children were overweight and at serious risk of developing life-threatening illnesses.
She believes that better diet and more of the right exercise can also help to stop social problems such as bullying and teasing in schools.
Dr Edmunds, a researcher at Bristol university and one of five experts advising the Government on child obesity, said: "About 11 years ago I was teaching science at secondary level at an inner London school, which was at the bottom of the league tables in Southwark. I asked myself, even then, why was I teaching so many overweight children? So I talked to a few of them and they all kept saying they hated PE and how horrible it was.
"Children should be more active but I don't think PE is the answer.
Changing is a nightmare and the actual lessons make children aware of their fatness.
"Parents are aware of basic nutritional knowledge but the biggest issue was being active."
She added: "If you go to a council estate you will see there are satellite dishes on every house because they don't cost much.
"It is easier and cheaper to eat badly and not be active. People with a limited amount of cash will find it expensive to live a healthy lifestyle.
Gym membership is expensive, eating fruit and organic vegetables is also expensive.
"We're seeing teenagers for the first time with type 2 diabetes. How many children have to get late onset diabetes before the Government starts to do something about it?" Dr Edmunds said schools need to do more to help.
"I've heard stories about some PE teachers whose attitude makes me shudder.
It seems that PE is geared for the 10 per cent who are sporty.
"We also need more equipment. I know that primary schools' budgets are low but perhaps they could use a bit more imagination.
"After the national curriculum came in schools became more concerned with the academic side, and physical activity was sidelined by the need to get children through Sats."
Dr Edmunds also wants to see more counselling, family therapy and parenting programmes to help obese youngsters.
"More children are becoming overweight so you would think bullying and teasing would get less. Yet it is getting worse. Society needs to be aware how to deal with this. A child may be overeating because they're grieving maybe because their dad has walked out or a grandparent has died."
One Brent school ran a pilot of extending the school day, giving students two-hour lunch breaks instead of one.
"The school brought in coaches at lunchtime and gave children the option of doing dance classes and martial arts among many other activities," Dr Edmunds added.