Wrong! All paediatric and psychological or psychiatric organisations accept ADHD. In fact, it is the most common mental disorder of children and adolescents.
Some people say, ADHD is not a real disorder because scientists cannot identify a cause of ADHD. The hyperactive behaviour of the children should be more or less "normal" like "ants in the pant" or signs of bad parenting or lack of motivation at school. These children could be stimuli driven due to a change of the environment like too much TV or a lack of attention of their parents.
One of these opponents is Thomas Armstrong. He says : "ADHD is a disorder that cannot be identified in the same way as polio, heart disease or other legitimate illnesses." But the diagnosis or psychological problems or psychiatric diseases like depression, anxiety disorders or dementia is not based on lab tests. Dr. Russel Barkley, a famous ADHD expert, explains that we do not have such tests for headaches, multiple sclerosis or Alzheimer. We would eliminate nearly all mental disorders, if we would only diagnose or treat "diseases" with a single lab test for diagnosis.
However, there is convincing evidence for a biological vulnerability of ADHD. Epidemiological evidence indicates that ADHD has a powerful genetic component. University of Colorado researchers have found that a child whose identical twin has the disorder is between eleven and 18 times more likely to also have it than is a non-twin sibling. Genetics is a special area of interest in the area of ADHD research. Scientists have identified several possible genes that influence the symptoms and severity of the disorder. Additional functional anatomy with SPECT or PET diagnosis can show distinct changes in the blood flow of ADHD adults and changes in the dopamine system (Dopamine transporter DAT) which are typical for ADHD. But this of course is not a method to diagnose ADHD in a clinical setting due to extreme high costs and possible adverse effects of the diagnostic tools (low radiation) for children.