This is the VOA Special English Education Report.

We continue our series on learning disabilities with a problem that is not considered a learning disability by itself, but it can af fect learning. Our subject is attention deficit disorder, A.D.D., and the related form A.D.H.D., attention deficit hyperactivity disorder. These affect an estimated five to ten percent of children worldwide.

Children who forget easily and never seem to finish tasks or pay attention might be found to have A.D.D. If, in addition, they seem overly active and unable to control their behavior, a doctor might say it is A.D.H.D.

Experts say the cause involves a chemical imbalance in the brain. It can affect not only school, but also personal relationships and the ability to keep a job later in life. Many of those affected also have learning disabilities or suffer from depression.

Medicines can produce calmer, clearer thinking for periods of time. But the drugs can also have side effects like weight loss and sleep problems. And there is debate about the morality of medicating children.

Susan Smalley is a psychiatry professor at the University of California, Los Angeles. She just led a study of A.D.H.D. in northern Finland. The study found that rates and signs of A.D.H.D. are about the same in children there as in the United States.

The Finnish children are rarely treated with medicine, while medication is widely used in the United States. Yet the study found that the two populations have few differences with A.D.H.D. among older children and teenagers.

Professor Smalley says medication is very effective in the short term. But she says the study raises important questions about the long-term effectiveness of current treatments.

The study also found that only about half the Finnish children diagnosed with A.D.H.D. had deficits in short-term memory and self-control. These cognitive deficits are generally considered part of the definition of A.D.H.D.

The study also found more evidence that A.D.H.D. symptoms change with age. Hyperactivity and lack of self-control decrease. But about two-thirds of children continue to show high levels of inattention as teenagers.

The Journal of the American Academy of Child and Adolescent Psychiatry published the study. 

Even if drugs are used, experts say children with A.D.H.D. also need other help. For example, they need to learn organizational skills, and they need supportive adults.

And that's the VOA Special English Education Report, written by Nancy Steinbach and available at voaspecialenglish.com. I'm Steve Ember.