Until this summer Michelle Burgess had never been particularly concerned about her daughter's intermittent and unspecific leg pains. After all, they occurred infrequently, came only at night and had always gone by the following morning. But when late one evening nine-year-old Krystal started getting such acute pains in her shins that she couldn't stop crying, her mother became suddenly alarmed. "She's had these pains in her shins on and off since she was two," says Burgess, "but this was different because she was absolutely beside herself with pain. Nothing could soothe her."

Burgess rang NHS Direct, but the doctor who took her call did not seem unduly concerned and recommended that she book an appointment with her GP. In order to eliminate anything "sinister", the GP booked Krystal in for blood tests and an x-ray at the local west London hospital. Unsure what these were for, Burgess sneaked a look at her daughter's notes and saw the word "sarcoma", a disease she was told meant cancer in the bone, connective tissue or muscle.

But the results of the tests were all normal; there was still no explanation for Krystal's pains. Then Burgess asked if they might be growing pains. The reply was unequivocal: "I don't believe in growing pains," said her GP. "In fact, I think they're a complete fallacy."

He's not alone. Devon GP John Bridge, similarly, has never diagnosed growing pains, believing it to be a term contrived solely to put parents' minds at ease. "It's just like teething," he says. "Older children who lose their milk teeth never complain about the pain when their new teeth come through, so why should teething cause pain and fever in babies? There has to be another explanation and it's the same with growing pains. I've always viewed them as a reassuring old-fashioned term that parents used once doctors had excluded anything more serious."

But not all doctors agree. One of the world's leading paediatric growth experts, Charles Brook, recognises growing pains as a very real and painful condition. "There's no doubt that they do exist," says Brook, professor of paediatric endocrinology at University College London medical school. "Children describe them very specifically, usually on the front of the thighs and down their shins, but never in the joints. If the pain is in the knees or hips, that indicates that the emphasis is in the joint and therefore should be investigated further."

One in four children suffer from benign, self-limited and unspecific aches and pains in their legs, but not all doctors put it down to growing pains. Indeed, the fact that there is no accepted medical name for the condition illustrates the medical profession's woolly attitude towards it.

Nicky Mayhew's daughter Sarah, now 13, suffered from severe pains in her legs between the ages of six and 11. "The pains were so bad they'd keep her awake at night and always reduce her to tears. Paracetamol syrup would take the edge off but not completely kill them. The doctor assured me that it was nothing serious and that, although the medical profession doesn't formally recognise growing pains, one of her children had the same problem. I always felt slightly uneasy about this - oh God, what if it turned out to be bone cancer and we hadn't done anything in time to save her? - but luckily she grew out of it."

So do growing pains exist, or is it just a useful term to reassure parents and comfort children? Perhaps the distinction is not so straightforward. Certainly, much of the distress that children feel with undefined pain comes from the worry that there is something wrong with their bodies. Although clinical psychologist Linda Blair doesn't doubt the existence of growing pains, in her experience when parents stop fretting about their child's pain, it can help to alleviate it. "It doesn't affect the pain directly, but it affects the child's reaction to the pain," she explains. "Too much fussing magnifies pain."

While no firm evidence exists to show that growth of bones causes pain (hence the medical establishment's manifest scepticism), long experience has shown that stretching limbs can be linked to unexplained pains. A child grows approximately 13cm in height between the age of one and two. The rate then slows to 5-6cm a year until adolescence, when there is a sudden spurt in growth to adult height. While the lengthening of bones and strengthening of muscles are the most apparent signs of growth, other tissues, such as connective tissue, teeth, body fat, skin and the nervous system, are also growing all the time.

The experience described as "growing pains" generally strikes in early childhood among three- to five-year-olds, and later in eight- to 12-year-olds. One in four children suffers from the pains, usually at night, when they are trying to sleep. For some, the pain is so severe that it wakes them. Massage, warm baths or paracetamol will usually relieve the symptoms.

One explanation is that growing pains are the result of overuse and muscle fatigue: the cumulative result of days or hours of hard play resulting in night-time muscle pain and cramping. Another theory is that the muscles or tendons are still a little too tight for the growing length of bones, resulting in muscle spasms.

But there are other, more serious conditions that can be confused with growing pains. One such is Osgoode-Schlatter's disease - a condition where the bony muscle below the knee cap becomes extremely tender; it usually affects teenagers at about the age of 13. "When you touch it, a child with the condition will practically jump off the bed in pain," says Brook, "and that certainly isn't the case with growing pains." Children whose pain is due to a specific medical condition do not like to be handled, since movement tends to increase the pain, whereas children with growing pains respond differently; they feel better when they are held, massaged or cuddled.

Although growing pains usually cease around the age of 11, that's not to say that adolescents don't suffer from similar non-specific aches and pains. According to Brook, "There is definitely such a thing as outgrowing your strength, meaning that children get bigger before they get enough muscle to deal with the leverage - this is particularly common among tall, lanky boys. The main force for generating muscle is testosterone, and until that starts to rise, there's often a disproportion between muscle bulk and length of limbs."

Sometimes growing pains are mistaken for chronic pain syndrome - long term, unexplained pain. "Any specific pain, particularly in the lower limbs, is more likely to be growing pains, but if the pain is changing, chronic, moving from here to there, then it's likely to be psychological," says Nick Barlow, consultant paediatric psychologist at Leicester Royal Infirmary. At the hospital's paediatric pain clinic, chronic pain syndrome is most common among adolescent, high-achieving girls, for whom the pain starts at puberty, shortly after the changeover to secondary school. "There's no physical evidence that anything is wrong with them," says Barlow, "but they're not functioning because of the perceived pain. A lot of adolescents who are afraid of failing fall into this category. They use the pain - which is very real - as a reason for not failing." Not growing pains then, but rather growing-up pains.

Part of any psychological intervention in this condition will be to ensure that the secondary gain from pain isn't so great that a child cannot give up the pain. What most eventually learn to do - whether the pain is caused by the physical strain of carrying heavy bags or the psychological strain of not coping at a new school - is learn to tolerate it. With adolescents complaining less of pain as they grow older, it may be that they come to realise that living with occasional and vague aches and pains is just part of adult life.