Hmm, what's it to be? A lentil korma with brown rice and salad, then fruit and a yoghurt for afters, or a High School Musical bag stuffed with crisps and a couple of bars of chocolate? It sounds absurd but in some schools children sitting next to eat other could be eating such contrasting lunches.

While school dinners have come on nutritionally in leaps and bounds, and thanks to more money for ingredients and training for the dinner ladies, they taste a whole lot better too, there's nothing to stop pupils in many schools bringing in junk from home. A survey last year lifted the lid on lunchboxes to reveal the unappetising truth: what's inside them contains too much saturated fat and up to half the daily allowance of of salt. [Kids under 7 should have no more than 3g of salt a day.] Salads are scarce and only half the children brought in a portion of fruit and vegetables.

Children who aren't eating school dinners are losing out - that's about 60 per cent of primary school kids. And this is why, as part of the Government's attempt to tackle obesity, Alan Johnson, the Health Minister, has suggested that schools should check lunchbox contents.

The School Food Trust, the body set up by the Government to turn round school dinners, suggest drawing up a policy for packed lunches - a few basic rules to bring them in line with a healthier school environment - and make sticking to it part of a code that parents have to agree to. Others say it is impossible for schools to police what children bring in to eat. Margaret Morrissey, of the National Confederation of Parent Teacher Associations, says: “Many parents in this country will feel that it is their decision what they feed their children.”

Joe Harvey, of the Health Education Trust, a charity involved in the Better School Food campaign, agrees. “You can't search kids for Kit Kats,” he says. So what can schools do about it? “There has to be a process of education and consultation or they'll get the burgers-through-the-fence brigade. It should be part of a whole school food policy.” He advises schools to build food rules into any contract the school makes with new parents; do everything possible to make sure children know what's going on in the school kitchen; and make the meal service as attractive as possible.

Meanwhile, the schools below have different ways of giving chocolate and crisps the cold shoulder in packed lunches . . .

THE HILL PRIMARY, BARNSLEY, SOUTH YORKSHIRE

“If we banned chocolate it would cause an uproar,” admits Sue Miller, a teaching mentor at The Hill Primary School in Barnsley, where 46 per cent of children qualify for free school meals. So although 60 per cent of children eat school food, and everything is being done to encourage more to follow suit, it leaves a 150-strong packed-lunch bunch.

Such is the unwelcome contrast between the wholesome meal provided by the school, and the array of chocolate, crisps and sugary drinks some kids bring in, that the two groups eat separately. After such a lunch, it's no wonder some of those who bring their own are on the ceiling in the afternoon. Miller admits too that many pupils suffer from poor dental health. Rather than being obese, some children seem malnourished, and while helping them to eat better is a priority for the school, heavy-handed measures could be counter-productive.

Instead of laying down the law about lunch they've taken a different tack: offering parents help. One afternoon a week, for a month, a group of ten learnt to make sandwiches, wraps and pasta salads with a community-health-funded trainer. Smoked mackerel, mayonnaise and sweetcorn was a revelation to mums more used to slipping a couple of chocolate bars into a lunchbox. As Miller says: “Once you break down the barriers, it's very easy to engage; they see us as supporting them.”

One boy who refused to eat fruit now relishes the cream cheese, ham and banana wrap his mum has been making since the course. Other parents are attending “cook and eat” training sessions held outside the school, which also helps to pave the way for the packed-lunch policy the school is about to introduce. After six months' consultation with staff, families and children - who've been surveying the contents of the lunchboxes - this will be the next step towards giving every child a better chance of a healthy meal in the middle of the day.

“In this area, a ban wouldn't work. You have to be tactful, and I can't see it being easy, but parents are taking on board the effect of fizzy drinks on behaviour,” says Sue. Perhaps one day chocolate will be history at The Hill without the school ever having to issue an edict.

Allenbourne Middle School, Dorset

The fact that 99 per cent of pupils at Allenbourn Middle School in Dorset bring in packed lunch is no reflection on the school dinners. There aren't any. When the school was rebuilt a few years ago the decision was taken not to allow for a kitchen and the 1 per cent of children who qualify for free school meals are provided with a healthy packed lunch by the local authority.

With no healthy hot meal to compare with the home-made offerings, it's just as important that the 600 9 to 13-year-olds understand what makes a good lunch. And not having anything cooked at school hasn't held back the children's food education. The school, rated outstanding by Ofsted, also has Healthy School Status, despite an apparently laissez-faire approach to what's in the lunchboxes. Biscuits, crisps and chocolate are all allowed. “If parents want to give kids a load of rubbish, we've got better things to do than ban crisps, but we appeal to their better instincts,” says Derek Brooks, the deputy head.

Carol Catton, the health education co-ordinator, agrees: “As soon as you say, ‘Thou shalt not have . . .' they want it. We don't expect them to come in with just carrots and grapes. A chocolate bar is allowed, if the rest of the balance is there.” She says persuasion, cajoling and giving information about what constitutes a healthy lunch is what works best.

Only fizzy drinks are banned. Even then, the school doesn't put it quite like that. “We would not expect the kids to have them,” Catton says. “But I wouldn't tell a child what they had was wrong, I'd ask them what else they were having during the day.”

Any parent running out of good ideas has a source of inspiration - other children's examples of healthy lunchboxes. In response to a survey carried out by the Parents' Association they wrote, photographed and illustrated recipes for wraps, pasta salads, smoothies, soup and sandwiches for an eye-catching booklet of ideas.

There are nutritional tips and shopping lists to help harassed parents on the supermarket trawl. Just like Jasmine's scrumptious cheese scones, it has gone down a treat.

Petchey Academy, Hackney, East London

At the Petchey Academy in Hackney, school meals are compulsory. What's more there's no choice. If it's smoked mackerel biryani, that's what the children eat, unless they have signed up for the vegetarian option. It helps that the school started from scratch only 18 months ago, and the pioneering 13-year-olds, the first of two years, have never known anything else.

“Before we opened, we made it a policy that food would be one of the central pillars of what we were trying to achieve,” explains the school's food manager, John Liversidge, a chef, who also teaches cookery to the children.

Parents must agree to the rules before their child starts at the school, and one of the conditions is no packed lunches, no snacks and only fruit to be brought into school. If a class goes on a trip, they take a packed lunch made by the school. Serving the midday meal at tables, family-style, teachers sitting with the children, encourages sociability, sharing and table manners. As Liversidge says: “They should learn to use a knife and fork.” And packed lunches, let alone bags of crisps, don't allow for this.

Draycott Primary School, Derby

When head teacher Helen Knott asked parents to desist from putting crisps in lunchboxes, Draycott Primary School, in Derby, made headlines. But not for the reasons she would have wished. As part of its effort to improve food quality and education, the school sent out a packed-lunch policy to parents, which included a note from the governors requesting an end to crisps. Chocolate bars had been made unwelcome a couple of years earlier and children had been successfully encouraged to bring in fruit instead. Knott applauds the chip-free school dinners but the majority of children bring in packed lunches, which may occasionally consist of nothing more than three bags of crisps. “Such poor provision affects how children perform,” Knott remarks.

A handful of disgruntled parents went to the local paper and their objections were duly reported as a mass rebellion. They pointed to the puddings available as part of the healthy school lunches and cried foul. A parent was quoted as saying: “I object to Josh's lunchbox being policed in this way. I prefer to say what he has.”

Knott insists that this small group of vocal parents isn't representative. Most parents support the school policy. With crisps and chocolate off limits for lunch, Knott insists, “the children are picking up the message. It is not our policy to upset a child and make them feel they shouldn't be eating something. Often it's other children who put their hands up to let us know someone has crisps. Then we send a little slip home asking parents to please refrain.” And, now, even the rebels comply.

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