Yet what if not one of these children actually has ADHD? What if their inability to pay attention and their impulsive behaviour actually masks a serious underlying condition that is going undiagnosed and untreated? What if we're drugging our children for something that doesn't exist?

That's what Chicago doctor Richard Saul argues in his deliberately controversial book ADHD Does Not Exist, which has just been published in Australia. ''Not a single individual - not even the person who finds it close to impossible to pay attention or sit still - is afflicted by the disorder called ADHD,'' Saul says.

Yet he sees people rushing to diagnose themselves with ADHD thanks to its high profile in the media and the fact it often ''makes a great excuse''. He sees doctors diagnosing it ''too easily'' in their patients, and prescribing anti-ADHD drugs after asking only a few questions.

''There is an epidemic of ADHD misdiagnosis,'' Saul says.

Rather than ADHD, he believes patients are likely to suffer from other conditions - such as poor eyesight, sleep deprivation, bipolar or learning difficulties - of which ADHD is merely symptomatic. He argues that once these underlying conditions are found and treated, the ADHD symptoms ''almost always go away''.

Australian doctors have branded Saul's claims ''dangerous'' and ''sensationalist'', saying there is a wealth of evidence that ADHD does exist. They say doctors here are far more cautious in its diagnosis and treatment than in the US.

''He's saying, 'my personal experience outweighs all the scientific evidence available to people, my information is going to be more persuasive because it creates fear and concern,' '' says Sydney University's Associate Professor Michael Kohn, a staff specialist at the Children's Hospital at Westmead who has worked with ADHD children for two decades. ''It's manipulative rather than informative and it may make people afraid to seek help.''

Yet some parents believe any exploration of what causes ADHD symptoms is helpful. ''I'm pleased they're continuing to look at and question the diagnoses that are going on,'' says Kim Forrester, whose son Daniel has ADD and daughter Sarah has ADHD. ''I wish they would find the answer because it is so difficult as a child … If they can be armed with knowledge earlier on in life, they can be the best version of themselves at seven, not 27.''

A child who has difficulty paying attention, struggles to follow instructions, is disorganised and forgetful, cannot sit still, does not like waiting, and talks non-stop, can be classified as having ADHD. In 1937, it was discovered stimulant drugs helped control this behaviour.

But according to Saul, who has worked in behavioural neurology and development for 50 years, there has been a ''staggering'' rise in ADHD diagnoses this century, with the number of school-age American children classified as ADHD up 40 per cent. Adults are also increasingly being labelled ADHD. In Saul's opinion, they do not all warrant this diagnosis.

''The ADHD diagnosis has become far too large and all-encompassing, resulting in too many people suffering from stimulant use and the delay or denial of the treatment that's actually right for them,'' he says. In Australia, estimates of the prevalence of ADHD in school age children has ranged from 3 per cent to 11 per cent in the past decade.

In a bid to stop the ''knee-jerk'' diagnosis of ADHD, Saul has identified more than 20 alternative causes of ADHD symptoms. They include sight and hearing problems, mood disorders, substance abuse, obsessive compulsive disorder, giftedness, learning disabilities and Asperger's.

Saul cites multiple case studies of patients who have come to see him claiming to suffer ADHD, only to be subsequently diagnosed with a completely different condition.

There is seven-year-old Aviva who is causing trouble in class, fidgeting, talking loudly, and always asking to go to the toilet when she should be copying work from the board. A paediatrician has diagnosed ADHD and put Aviva on medication, to which she is reacting badly. Saul opts for eyesight and hearing tests, which reveal Aviva suffers from near-sightedness. She gets glasses and her behaviour immediately improves.

Nine-year-old Bhavik is also disruptive in class and his teacher suspects ADHD. Bhavik's behaviour is not a problem outside school, he is a top academic performer, and he tells Saul he always feels bored in class. Saul sends him for IQ testing, which reveals he's in the top 2 per cent of students, classifying him as gifted.

Such stories ring true for Forrester, who says her children have had eyesight difficulties, are gifted intellectually, and mental illness does run in her family.

But Kohn from the Sydney Children's Hospital says the way Saul advocates assessing ADHD symptoms in patients is ''routine'' in Australia. To be diagnosed with ADHD here, children must display inattention and/or hyperactivity symptoms for at least six months, according to the National Health and Medical Research Council clinical practice guidelines.

The symptoms must have been present since early childhood (before age seven), and must affect their behaviour at school, at home or socially. Significantly in the context of Saul's argument, there must also be ''no better alternative explanation'', such as another mental disorder, for the symptoms.

''A child/adolescent who meets diagnostic criteria for ADHD may not be always best served by making that diagnosis,'' the guidelines state. ''For example, their behaviour could be understood as a reaction to specific cognitive difficulties or family/environmental circumstances.''

University of NSW professor of child psychiatry Florence Levy says the question of whether ADHD exists as a standalone condition or is simply symptomatic of another illness has been debated ''off and on'' for a long time.

''Some underlying conditions can manifest with symptoms of attention and impulsivity/hyperactivity problems … Also, you can have traits which mean they have difficulty in developing the capacity to sustain attention over time. ADHD can be either a category or part of a continuum.''

She says some children can present with ADHD symptoms that are actually a delay in maturation that fixes itself over time.

Australian doctors say diagnoses of ADHD and the prescription of drugs to treat it have not spiralled here in the way they have in the US. ''In Australia it has not increased to the same extent,'' Levy says. ''I think we're a bit more conservative.''

Kohn says parents usually bring their children to see him when the situation has reached crisis point, not because they are looking for a quick fix. ''They've been suspended from school, there are fights at home, their education is being affected, their acting out has caused a crisis.''

He says scientific studies prove ADHD is a genuine medical condition, with evidence of biological changes in the brains of ADHD sufferers, and noticeable improvements in their behaviour when treated with medication.

He says ''robust'' brain imaging studies of people with ADHD have shown changes in the part of the brain that governs what a person knows and how they feel. ''The brain functions are not working efficiently or effectively.''

Doctors prescribe stimulants like Ritalin for ADHD sufferers to increase their attention span and reduce their impulsiveness. Prescriptions for Ritalin and other drugs to treat ADHD rose 72 per cent in Australia between 2000 and 2011, a study published in the British Medical Journal found.

Saul is alarmed at doctors' readiness to prescribe these drugs for children, and the rise in older people seeking ADHD drugs simply for a ''boost'' during exams or when they are working long hours. He argues that, over time, the body develops a tolerance of the drug, forcing doctors to prescribe higher dosages to achieve the same effect.

''Rates of stimulant use have risen dramatically,'' he says. ''Misdiagnosis of ADHD is a big part of this trend, but equally guilty is the increase in stimulant-seeking behaviour.''

Despite the angst about drugging children, Kohn says medication remains the ''single best treatment'' for ADHD, with two-thirds of his patients benefiting from being medicated. ''To control the symptoms and increase the function, you have to alter the biochemistry of the brain,'' he said. ''The majority of kids get prescribed [drugs]. Paediatricians think about that as the first line of defence.''

Forrester delayed putting her son on medication for two years after he was diagnosed with ADD. She had noticed when Daniel was two he was always on the go, constantly asking questions and interrupting people, but it wasn't until he started school she realised that marked him out from other children.

Daniel's year 3 teacher suggested his parents get him tested, and he was diagnosed with ADD. He started on half the recommended dose of Ritalin when he began high school.

''I didn't want to medicate my child; I put it off for so many years,'' Forrester says. ''He was suffering at school, he was socially an outcast and he was being labelled a naughty boy in class. I wanted him to go to school feeling confident rather than being growled at by the teacher and sniggered at by children.''

Forrester says Daniel loves the change Ritalin made. ''Personality-wise, he was absolutely still my son, but I saw he was much more focused. Socially he became more active and more accepted, and his teachers gave him glowing reports.''

Daniel has gone off Ritalin this year, to see if he can manage his symptoms himself. Now Forrester is considering whether to put her daughter on medication, as she has just been diagnosed with ADHD.

''I've suspected it for some years,'' she said. ''She's a gorgeous, sparkly little bundle of sunshine, but … She loses things, she forgets things, she constantly changes her mind. She gets bored and will talk your ear off.''

Levy believes pressures in today's society are prompting parents to seek medical explanations for their child's issues. ''There are pressures in terms of academic performance and pressures on families which are contributing to children's development problems,'' she says. ''… Parents want the best for their child, and as society becomes more pressured they look for diagnoses. If they think something might help their child cope in school they'll look into it.''

Forrester wants the medical profession to explore Dr Saul's provocative theories. ''At the end of the day it's about the child … The rest of it is secondary.''