Girls at primary school should be made to wear trousers and trainers and football should be banned from sections of the playground to encourage girls to stay active for longer and help tackle obesity, according to a new study.

Research into the way girls play at school has shown that impractical clothing including shoes that slip off can prevent them taking part in energetic games involving running and jumping.

But the study, by Carrie Paechter at Goldsmiths, University of London, also found that a typical playground dynamic involves football games played almost exclusively by boys taking over most of the space leaving girls as static observers.

Those who join in football games are labelled tomboys and risk their popularity among female friends, while also frequently not being accepted as fellow players by their male classmates.

Professor Paechter's research, funded by the government through the Economic and Social Research Council, followed two groups of nine to 11-year-old girls as they moved into year six, their final year at primary school. One school was in central London, with restricted playground space, while the other was in a leafy suburb on the outskirts of the capital with extensive playing fields.

The pattern was the same in both locations, the report finds. "In year five, most of the girls are still running around. But by the time they get into year six they have stopped moving and stand around and chat."

The study found that girls judged each other according to how active they were, and those who opted to join in boys' football games were seen as less feminine. "For some girls, physical immobility was seen to be an important marker of femininity, severely restricting their activity as they sought to establish themselves as mature and desirable," the report says.

"You either have to be an honorary boy in which case you have to reject femininity, or you have to be at least partly girly-girl," Professor Paechter said.

Where girls did join in football, boys would frequently not pass the ball to them, and they usually ended up clustered only in defensive positions rather than as prominent goalscorers.

More than a quarter of schoolchildren are now overweight or obese by the time they go to secondary school. Earlier this month a study at the University of Michigan found a direct link between obesity among girls and the onset of premature puberty.

"We have to understand that we're catching up with the States - there's a very small window in which we can do something about this," said David Haslam, clinical director of the National Obesity Forum, reacting to the findings.

Only only one in 10 UK children now walks to school, according to the Department for Transport, and the number driven to school has doubled in the last 20 years. Children spend on average more time in the car than they do taking exercise in PE lessons.

One way to address the problem, says the study, is for schools to be "more proactive about encouraging girls to maintain physical activity". It adds: "This includes encouraging or even compelling all children to wear clothes suitable for active play, such as sweatshirts, trousers and trainers."

Prof Paechter said: "I do think trainers should be compulsory in all playgrounds. It won't go down well with girls or parents, but girls would be able to move around a lot more readily."

Both schools in the study introduced girl-only or girl-majority netball, successfully bringing more girls into organised sports teams - often preferred by girls to active play at playtimes where peer pressure kept them sedentary.

The report also recommends more careful consideration of the use of space in playgrounds, including fencing off areas for football, laying out markings and equipment for other games and landscaping to get rid of large areas of open space.

"Increased provision of sports other than football, supported where possible by staffing, would encourage girls to take up such activities and remain active into adolescence," says the study. It also recommends "enforcing mixed hockey, football and rugby", and the provision of school sports labelled as gender neutral, such as adventure activities and cross-country running.

One school, St Elizabeth Catholic primary in Tower Hamlets, east London, recently banned football two days a week, substituting it with team games supervised by dinner ladies. "We wanted to ensure that all children were encouraged to participate," said acting head Carolyn Lindsay. "You obviously can't insist, but we can encourage and reinforce, and most children join in."

Childhood obesity

· There are around 1 million obese British children under the age of 16, according to the British Medical Association

· US research found that girls who are obese at four are significantly more likely to hit puberty by the age of 10

· From 1995 to 2004, obesity among girls aged 11 to 15 rose from 15% to 26% and for boys from 14% to 24%

· Children as young as three are being treated for obesity. In the average child, 20% to 25% of body weight will be fat, but specialists report some toddlers with up to 50% body fat

· Soaring obesity has led to a rise in childhood type II diabetes and will lead in future to more heart disease, osteoarthritis and some cancers