Some do have actual problems that need medical attention but ignorance on the part of medical professionals treating them plus pharmaceutical companies IMO unethical pressures lead to a massive misdiagnoses and gross over prescribing of unnecessary medications.
ADD ADHD is there BUT there is a more common set of disorders {they can test for and confirm} called Central Auditory Processing Disorders. The symptoms mimic closely ADD ADHD and it takes either a trained Speech Pathologist or Audiologist to diagnose it. If you ask a shrink about C.A.P.D. you're gonna get a blank stare. C.A.P.S. is sensory damage or dysfunction believed to be caused from such things as chronic ear infections or chronic allergies that can damage a kid or adults Inner Ear.
There is a lot of information on CAPD out there. The best part is that the information comes far removed from Mental Health and even in most cases Pharmaceutical Company influences. Vestibular Research holds some answers but here is a clear danger the Mental Health pro's better face and understand. If you give a child or an adult who has sensory or motor sensory dysfunction drugs that can over tax their sensory system or cause a Serotonin migration to the brain, you stand a good risk of an adverse medication reaction called Serotonin Syndrome.
Serotonin is a chemical 98% contained in the stomach used for promoting digestion. The other 2% is located either in the brain or blood stream. When an adult or kid is given SSRI's and has this reaction the person can go psychotic even in the early stages {first few days of SSRI usage}.
It is a very real reaction and the person is not responsible nor can they control how they react to it. It is the same as giving them LSD maybe worse. Their hallucinations which can last up to 3-5 days from stopping the medication is their reality.
I don't argue the fact some adults need antidepressants as I have seen the good they can do. But I have also watched in horror for nearly a week someone in acute Serotonin Syndrome induced twice because the doctors insisted she needed more Zoloft.
The simple fact is doctors today do not do basic medical history & work ups to catch basic what used to be common problems and treat them. If a kid has an ear infection history, Chronic tonsilitus, Chronic streph Throat, vision dysfunction, trouble understanding you, and or sinus allergies, and acts like they have ADD ADHD they likely don't need Ritalin or an SSRI then.
They are acting out because their audio/visual sensory flooding & saturaterad environment is triggering them to act out. TV's can do it. Video games can do it also. A noisy class room is one they can not learn in. They can not listen and take notes etc. The behavior is caused by the frustration and agitation of multi-tasking which may be an impossibility or near impossibility for them. When that is understood & dealt with properly the symptoms subside somewhat and behavior improves. If not and they get prescribed sensory enhancers you can have a kid or adult ready to do harm to others.
It is more common simply because the triggering conditions are more common. This has been here since man likely. But todays technology is placing some kids and some of us adults into a world that is overtaxing our abilities to process the audio & visual events around us. The result can be Cognitive Behavioral Problems. That means depression, anxiety, agiation, and other reactions. Here is a great description a long read but worth it.
COGNITIVE ASPECTS OF VESTIBULAR DISORDERS
The Mental Health Profession does not look for this problem nor do many family doctors who refer a kid to a shrink.