Children who are naughty, bored or fidgety are being wrongly diagnosed with a behavioural disorder when they are simply younger and less mature than their peers, a study suggests.
Attention deficit hyperactivity disorder — known as ADHD — is characterised by inattentive, hyperactive and impulsive behaviour — and experts believe it affects up to 400,000 British children.
But a major study has suggested many children may be being mistakenly diagnosed with the disorder.
Researchers at the University of Nottingham found that those in the same school class were far more likely to be diagnosed with ADHD if they were the youngest in the year group. Writing in the Lancet Psychiatry journal, they said when children are very young, an age variation of just 12 months in a class can result in a large difference in maturity.
The study, which used population data from all children in Finland born between 1991 and 2004, found that younger pupils in a class were significantly more likely to be diagnosed with ADHD.
Children under the age of ten who were born in the last four months of the school year were 64 per cent more likely to be diagnosed with ADHD than those born in the first four months of the year.
The study found that the disparity could not be explained by other behavioural or developmental disorders. Professor Kapil Sayal, from the Institute of Mental Health in Nottingham, said: The findings of this research have a range of implications for teachers, parents and clinicians. With an age variation of up to 12 months in the same class, teachers and parents may misattribute a child's immaturity.
"This might lead to younger children in the class being more likely to be referred for an assessment for ADHD. Parents and teachers as well as clinicians who are undertaking ADHD assessments should keep in mind the child's relative age."
He called for greater flexibility in school starting dates for younger children who may be less mature than their peers.
"From an education perspective, there should be flexibility with an individualised approach to best meet the child's needs,' Professor Sayal added.
Evidence suggests that roughly 5 per cent of children around the world develop ADHD.
But the researchers said the chance of being diagnosed with the disorder varies significantly country to country.
They say this inconsistency may be because adults benchmark' the development of younger children and compare them against older peers in the same year group. They may then inadvertently interpret immaturity as a more serious problem.
Some 100,000 British children are diagnosed with ADHD, and the problem is rapidly growing.
Experts believe up to 7 per cent of British children, or 400,000, have the condition, meaning three quarters may be undiagnosed.
Prescriptions for ADHD medications in England rose rapidly from 1997 to 2012, NHS figures show.
Treatments include therapy and medication such as the central nervous system stimulants Ritalin and Dexamfetamine but there is no cure.
Attention deficit hyperactivity disorder, ADHD, is a group of behavioural problems including inattentiveness, hyperactivity and impulsiveness.
Symptoms tend to be noticed at an early age and often get worse when a child starts school.
Most children are diagnosed between the ages of six and 12.
Between 2 to 7 per cent of British children are thought to have ADHD up to 400,000 but only 100,000 have been diagnosed.
The exact cause is not known but it tends to run in families and scientists believe the primary cause is genetic.
Premature or small babies are also more likely to develop ADHD.
The problem is likely to be missed among girls, whose disruptive behaviour is less obvious.
There is no cure but the disorder can be managed with therapy and medication such as Ritalin.
Prescriptions for ADHD medications in England rose from 92,100 in 1997 to 786,400 in 2012.