There is no universally recognized definition. It is sometimes defined, though, as a disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence and sociocultural opportunity. The only trait that children with dyslexia have in common is that they read at levels significantly lower than is typical for children of their age and intelligence. This reading lag usually is described in terms of grade level. Most experts agree that a number of factors probably work in combination to cause dyslexia, though the exact cause is not known.
Some experts believe that dyslexia is caused by the methods used to teach reading.
In particular, they blame the whole-word method that teaches children to recognize words as units rather than by sounding out letters. Some researchers attribute dyslexia to psychological or emotional disturbances resulting from inconsistent discipline, absence of a parent, frequent change of schools, poor relationships with teachers or other causes. Obviously a child who is unhappy, angry, or disappointed with his or her relations with parents or other children may have trouble learning. Although emotional stress may not produce dyslexia, stress can aggravate any learning problem. A number of investigators believe that dyslexia results from alterations in the function of specific parts of the brain.