Some children with ADHD may simply be more immature than their peers, according to a study.
Researchers found that the youngest children in a school year are more likely to be diagnosed with the condition.
They said it means "developmental immaturity" may be an underlying factor when children are assessed for attention-deficit hyperactivity disorder.
The condition is estimated to affect up to five per cent of children while one per cent are considered to have a severe form of ADHD.
The number of diagnoses and prescriptions has increased significantly in recent years, up from around one per cent in the 1990s.
The study looked at 378,881 children admitted to schools in Taiwan, both pre-school and primary age and teenagers.
Researchers found that youngsters born in August had a higher risk of being diagnosed with ADHD and receiving medication for the condition.
The number of boys diagnosed with ADHD who had been born in August was 4.5 per cent compared to 2.8 per cent for those born in September.
It found 1.8 per cent of girls born in September had the condition, but among those born in August it was 2.9 per cent.
However, when the statistics were broken down by age, researchers found adolescents born in August were not at an increased likelihood of being diagnosed. The researchers said this finding, which is consistent with previous studies in the US and Canada, suggests the older a child gets, the less likely it is that their birth month has an impact on their being diagnosed.
Their study raises the possibility that some children may be diagnosed simply because they are younger and less mature.
Lead author Dr Mu-Hong Chen, whose research is published in the Journal of Pediatrics, said: "Our findings emphasize the importance of considering the age of a child within a grade when diagnosing ADHD and prescribing medication to treat ADHD."
The month in which a child is born has also been found to affect educational achievement, with older pupils getting better grades than their younger peers, as well as performance at sport.
Dr Kuben Naidoo, chairman of the ADHD Foundation and a consultant psychiatrist, said:
"The findings of this study are most interesting but must be treated with a degree of caution particularly with regard to conclusions about possible reasons for the differences seen in younger children compared to adolescents." He added: "In the UK setting the assessment and diagnosis of ADHD across the lifespan is robust and relies on information gathered from a number of sources including the family and school.
"This is then coupled with information obtained from a clinical interview by a specialist paediatrician or psychiatrist.
"The option to treat with medication is not taken lightly and consideration is also given to psychological strategies to support the individual.
"This decision on the type of treatment would be influenced by the degree of impairment experienced by the individual.
"The issue is not as simple as assuming that age, as an indicator of neurocognitive maturity, influences ADHD symptoms as we do see a significant number of adults presenting to psychiatric services for the first time with symptoms of ADHD."
The condition is a controversial area of medicine. Some critics argue that the rise of ADHD is down to social factors rather than more effective diagnosis of a biological condition.
Peter Conrad, a professor at Brandeis University in the US, said that the rise of ADHD in the UK and other countries had been triggered by more aggressive marketing by drug companies. He said they were following the US trend to 'medicalise' behaviour.
In France, diagnoses of ADHD are just 0.5 per cent because it is recognised less as a biological condition.
How ADHD used to be "cured"
A similar condition to attention deficit hyperactivity disorder was first described in Germany in 1775.
Suggested cures included cold baths, steel powder and gymnastic exercises.
ADHD was first named by psychiatrists in 1987, having previously been called hyperactivity.
To be diagnosed today, children need to have six symptoms on a list of 18, such as impulsivity, fidgeting and talking excessively.
Treatments include drugs such as Ritalin, prescriptions for which have soared from 359,100 in 2004 to 922,200 last year.
Recent research has found that the condition continues for many into adulthood - with a famous case being Scottish impressionist Rory Bremner.