Encyclopedia / D / Dyslexia



Dyslexia is an impairment of the ability to read, as a result of a variety of pathologic conditions, some of which are associated with the central nervous system.


Dyslexic persons often reverse letters and words, cannot adequately distinguish the letter sequences in written words, and have difficulty in understanding left from right.

Some reading experts doubt that dyslexia is a pathologic disorder and believe the condition represents a combination of reading problems, each of which should be isolated by specific tests. The problems cited by these authorities are poor vision, impaired hearing, emotional immaturity, lack of physical development, psychic stress, and inadequate reading instruction.

Over the years, the term dyslexia has been given a variety of definitions, and for this reason, some teachers have resisted using the term at all. Instead, they have used such terms as "reading disability" or "learning disability" to describe conditions more correctly designated as dyslexia.

Although there is no universally recognized definition of dyslexia, the one presented by the World Federation of Neurology has won broad respect: "A disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence, and sociocultural opportunity."


Developmental dyslexia is a specific learning disability characterized by difficulty in learning to read. Some dyslexics also have difficulty learning to write, to spell and, sometimes, to speak, or to work with numbers.

We do not know what causes dyslexia, but we do know that it affects children who are physically and emotionally healthy, academically capable, and who come from good home environments. In fact, many dyslexics have the advantages of good schools, high mental ability, and parents who are well-educated and value learning.

School children are subject to a broad range of reading problems and researchers have discovered the cause of many of these problems. Today, most teachers accept these research findings and use them in planning their instruction, but there remains a small group of children who have difficulty in learning to read for no apparent reason. These children are called dyslexic. Although estimates of the prevalence of dyslexia are hard to find, it is estimated that as many as 15 percent of American students may be classified as dyslexic.

Dyslexia tends to run in families.


Children with dyslexia are not all alike. The only trait they share is that they read at levels significantly lower than is typical for children of their age and intelligence. This reading lag is described in terms of grade level. Dyslexics commonly have one or more of the following problems:

  • Difficulty learning and remembering printed words
  • Letter reversal (b for d, p for q), number reversals (6 for 9), and changed order of letters in words (tar for rat, quite for quiet) or numbers (12 for 21)
  • Leaving out or inserting words while reading
  • Confusing vowel sounds or substituting one consonant for another
  • Persistent spelling errors
  • Difficulty writing

Other characteristics sometimes include:

  • Delayed or inadequate speech
  • Trouble picking the right word to fit the meaning desired when speaking
  • Problems with direction (up and down) and time (before and after, yesterday and tomorrow)
  • Clumsiness


A physician will obtain a medical history and perform a physical exam in order to rule out other causes of reading difficulty, including vision problems. Testing by a psychologist is often recommended.


Educators and psychologists generally agree that the remedial focus should be on the specific learning problems of dyslexics. Therefore, the usual treatment approach is to modify teaching methods and the educational environment.

Children suspected of being dyslexic should be tested by a psychologist. By using a variety of tests, it is possible to identify the types of mistakes that are most commonly made. The examiner then can make specific recommendations for treatment such as tutoring, summer school, speech therapy, or placement in special classes.

Treatment programs for dyslexic children fall into three general categories: developmental, corrective, and remedial. Some programs combine elements from more than one category.

The developmental approach involves the use of methods that have previously been used in the belief that these methods are sound and that the child needs extra time and attention.

The corrective approach uses small groups in tutorial sessions, but it emphasizes a child's assets and interests. Those who use this method hope to encourage children to rely on their own special abilities to overcome their difficulties.

Proponents of the remedial approach try to resolve the specific educational and psychological problems that interfere with learning.


How do you know if this is dyslexia or some other impairment?

What tests need to be done to determine the cause of the learning disability?

Do these tests indicate causes of dyslexia?

At what age do you recommend testing?

What treatment program do you recommend?

Who in the community is doing the best work with persons who have dyslexia?

Will any of these programs instruct us, the parents, on how to work with our child?

Are most of these programs offered in public schools?

Should a psychologist be seen? And for how long?

What is the prognosis?

Some current research is focusing on the ability of computerized devices to assist those with dyslexia to read or otherwise function in environments where skill with written words is essential.