Thousands of children with attention deficit hyperactivity disorder are "slipping through the net" because teachers are not trained to identify the syndrome.
Girls are most at risk of being undiagnosed, according to a report by the County Durham and Darlington child and adolescent mental health strategy and Durham university.
"It's clear that children, particularly girls, are slipping through the net," said Professor Peter Tymms, one of the report's authors and director of the curriculum, evaluation and management centre at Durham. "I think teachers are more inclined to identify boys as being impulsive or inattentive. The girls might be able to hide it more."
ADHD children behave in hyperactive and impulsive ways and have difficulty concentrating. It is believed that up to one in 20 pupils in Britain (about 400,000) have some level of ADHD, but only a fraction of those are diagnosed.
The National Attention Deficit Disorder Information and Support Service estimates that between 30,000 and 40,000 children are on medication to control the disorder. While the number of children prescribed drugs such as Ritalin is rising, experts believe this is due to greater awareness of the syndrome, not an increase in the number of sufferers.
However, some people believe that ADHD is an over-used label given to unruly children.
Figures show that 314,500 prescriptions were written last year for Ritalin-type drugs, up from 92,000 in 1997.
The Durham report states that the prevalence of ADHD is up to four times higher among boys than girls.
Professor Tymms said learning about ADHD should be part of in-service training for teachers, as early detection was vital.
One school with a strong emphasis on training to help teachers recognise the condition is Woodchurch high specialist engineering college, on the Wirral. It prides itself on its policy of inclusion and its work with students with medical and physical impairments.
"Students with ADHD are not just naughty. They have an impairment as great as children who use a wheelchair or who have been diagnosed with autism,"
said deputy headteacher Rebekah Phillips.
Two teenagers who have benefited from the school's approach are Year 10 pupil Daniel Lamb, 14, and Year 11 pupil Craig Higginson, 16.
Daniel was diagnosed with ADHD at the age of seven, and has battled with behavioural problems for years. His mother, Christine Parkins, said the school had helped him settle down and learn.
Craig, who takes medication to control his behaviour, said: "They (the teachers) talk to me about my behaviour and they help keep me focused on what I'm doing."