One in 20 young people are said to have attention deficit and hyperactivity disorder. No doubt, many of them are at times extremely restless, inattentive and hard to engage in learning.

Yet is it accurate or helpful to say they have ADHD? The term is used so often and with such seeming certainty that it appears to have a real meaning, which remains the same in any time or place. But is the meaning exact or unchanging?

Other kinds of special educational needs are also discussed as if they were a medical illness. First, the need or problem is seen to be within the child. Second, it should be identified by an expert. And third, the problem should be named or diagnosed so that it can have the correct treatment.

Each point is questionable.

Most doctors diagnose illness in ways that do not fit special educational needs. They look for a medical “sign”, such as a virus or a tumour. Test results prove visibly when an illness is present. Cancer doctors do not need to meet to decide by vote whether or not lung cancer really exists.

Instead of using medical guesswork, they rely on the same test results anywhere in the world to prove when a patient has lung cancer.

ADHD does not have any medical sign or proof. Evidence on brain scans is cited, but so many children scanned are on medication that it is not known whether the treatment or the supposed condition has altered the brain.

Since 1970, ADHD has been thought of as an illness because American psychiatrists voted to include it in their directory of diagnoses, first as ADD, later as ADHD.

Attention deficit and hyperactivity disorder also varies from illnesses, like cancer, in being quite recently discovered, in the suddenly soaring rates of cases and in the greatly varying rates between countries, even regions. A real illness that is genetic or acquired could not vary so much.

Nine million children in the United States are treated by pills for what is described as the chemical imbalance of ADHD. No one knows what chemicals are involved.

The rising use of Ritalin in the treatment of attention deficit and hyperactivity disorder can be seen as part of a wider movement to turn other aspects of human life into illnesses in need of pills: sexuality, being too shy, or fat or thin, or too active. This narrowing of what is supposed to be normal greatly widens the scope for perceiving people as special or different who would once have been accepted as normal.

ADHD is vaguely defined as a collection of behaviours, such as being inattentive or impulsive. It is sometimes tested by asking children to read a very boring text and seeing how long they continue. Should we think of children as sick when they quite reasonably point out that a task is inappropriate, or resist because they are frustrated? Most ADHD behaviours could apply to anyone at certain times, when we feel bored or stressed. And if there is no medical sign, are doctors the best people to identify whether children have SEN, an educational concept, or attention deficit and hyperactivity disorder, a behavioural one?

Unlike lung cancer, the meaning of SEN depends on the context. Special educational needs simply means extra needs that are not catered for in the average school. In schools that are adapted for children who use wheelchairs, or speak Chinese, their needs are not special or different.

The hyper in ADHD means too much, but how much is too much? Until around 1800, when machines began to replace muscle power, people needed high amounts of energy to survive. To create a loaf of bread took months of heavy labour. Ploughing, sowing, reaping, carting, winnowing, milling, kneading, these were some of the tasks that adults and children shared, and energy was valued.

Of course, there are many young people with physical and mental problems who benefit greatly from medical care. But there are many others who are not ill and who are harmed by the medical model, which assumes that the problem is in the child - or is the child.

Inclusive schools, like inclusive employers and communities, can overcome barriers and prejudices to enable disabled people to share a more equal place with others and not to be special. Causes for the apparently rapid rise in ADHD rates might include the way school playgrounds and playing fields have been sold. Playtimes are shorter. School meals and vending machines offer high calorie foods with additives that work as stimulants.

The maths and literacy hours and the national curriculum assume that young children can and should sit still for long periods, with little say in what or how they learn. Many children have few times and spaces for adventurous outdoor play. Few children walk to school. Play spaces have been made safe yet unchallenging. Privatised leisure centres are expensive. The police stop young people gathering in parks when there is nowhere else for them to enjoy group activities.

How many children seem hyperactive because they are expected to be too passive? Do special needs result not from the children, but from the way they are treated, especially the more restless and energetic ones? If so, effective treatments must involve adults working with children and young people to turn schools into more healthy and inclusive places.

Priscilla Alderson is professor of childhood studies, Institute of Education, University of London