Centre for Educational Research and Innovation - CERI

Primer on Dyslexia


Dyslexia Primer


Christina D. Hinton

The purpose of this primer is to answer frequently asked questions regarding dyslexia and direct the reader towards further resources on the subject.

Christina Hinton works on issues at the nexus of education and neurobiology in affiliation with the OECD and Harvard Graduate School of Education. The following is, in great part, taken from “Overcoming Dyslexia” by Sally Shaywitz (Knopf, 2003).

What is dyslexia?

The word “dyslexia” is derived from the Latin word “dys,” which translates to difficult, and the Greek word “lexia,” which translates to words; it literally means, “difficulty with words.”  Dyslexia is a neurobiologically-based language impairment defined by a difficulty in reading that does not result from global intellectual or motivational deficits (Lyon et al., 2003; Shaywitz, 2003; Shaywitz & Shaywitz, 2005).  It has formally been defined as follows:

Dyslexia is a specific learning disability that is neurobioligcal in origin.  It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and encoding abilities.  Their difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction (Lyon et al., 2003).

Dyslexia is a variable and multifaceted learning disorder.  It occurs along a continuum of reading ability and inability (Shaywitz et al., 1992).  Therefore, dyslexia exists in gradations, and its severity varies among affected individuals.  Symptoms of dyslexia often affect both oral and written language, reflecting a basic difficulty in accessing the basic sounds of language. (See below for specific indicators that can help identify dyslexia).

Dyslexia is an isolated language impairment that occurs independent of intelligence (Shaywitz, 2003).  Higher-level thought processes, such as reasoning, problem solving, comprehension, concept formation, and critical thinking are not directly disrupted by dyslexia.     

What causes dyslexia?

While there has been some debate concerning the cause of dyslexia, several lines of converging evidence suggest that dyslexia is caused by a localized impairment in the phonological module, the functional part of the brain responsible for processing sound elements of language (Shaywitz, 2003; Shaywitz & Shaywitz, 2005).  According to this phonological model, dyslexia results from an impaired ability to segment spoken words into phonologic parts and link each letter to its corresponding sound (Shaywitz, 2003; Shaywitz & Shaywitz, 2005).  Phonomes are small units of sound that can be conceptualized as the building blocks of words (for example, the word cat is comprised of three phonemes: k, aaaa, and t).  In individuals with dyslexia, phonemes are less well defined.  Shaywitz (2003) characterizes such phonemes as carved letter blocks with faces so worn that their letters are no longer prominent.  This lack of precision results in difficulties appropriately retrieving and manipulating phonemes.  Individuals with dyslexia also struggle with what is known as the alphabetic principle (Shaywitz, 2003).  This principle refers to the notion that written and verbal words are comprised of the same phonemes, and that letters in words map onto phonetic sounds.  An understanding of this principle enables verbal and written words to be segmented (taken apart) and blended (put together), processes necessary for decoding written text.                

Functional imaging studies have revealed a potential neural substrate for the phonological deficit thought to underlie dyslexia.  There appears to be a disruption of two left hemisphere posterior brain systems, one parieto-temporal, the other occipito-temporal (Shaywitz & Shaywitz, 2005; Shaywitz et al, 2001). 

There is an alternative model of dyslexia, known as the magnocellular theory, which attributes dyslexia to dysfunction of cells involved in processing sensory information (Stein & Walsh, 2003).  This theory posits that the disruption of these cells results in auditory, visual, and/or motor difficulties, and these difficulties are the primary cause of dyslexia.  However, sensory dysfunction is absent in many cases of dyslexia, and has no clear causal link to reading problems (Ramus, 2004; Ramus, 2003).  By contrast, phonological processing deficits are consistently found in individuals with dyslexia (Morris et al., 1998; Ramus et al., 2003).  Further, there is evidence indicative of a correlative relationship between phonological and reading problems, as well as a cogent neurobiological explanation of how phonological processing problems could lead to reading difficulties (Lundberg, 2002, Pennington & Lefly, 2001; Shaywitz, 2003; Shaywitz & Shaywitz, 2005).  It seems most plausible that dyslexia is caused by a specific phonological deficit that is optionally accompanied by confounding sensory dysfunction (Ramus, 2003; Stuart, 1999).   

Will children “grow out of” dyslexia?

Dyslexia is not a transient lag in development (Bruck, 1992; Francis et al., 1996; Shaywitz, 2003).  It is a persistent condition that will not fade away with brain maturation.  It is critical that children at risk for dyslexia begin treatment as early as possible.  While results of later intervention are significant, results of early intervention are more rapid and successful (Lyytinen et al., 2005; Torgesen, 1998).   

Is dyslexia hereditary? 

Dyslexia is often hereditary (Pennington & Gilger, 1996; Lyytinen et al., 2005).  Between twenty-three and sixty-five percent of children with dyslexia have a parent with the disorder.  Replicated linkage studies of dyslexia implicate loci on chromosomes 2, 3, 6, 15 and 18 (Fisher & DeFries, 2002).  Future genetic research may identify reliable predictors of dyslexia, which would allow for preventative interventions that can reduce the detrimental effects of the disorder (Lyytinen et al., 2005).

If dyslexia is brain-based and hereditary, is treatment futile?

The notion that genetically-influenced, brain-based characteristics are deterministic and fixed is a dangerous misconception.  The structure of the brain is a function of a synergistic interaction of genetics and experience.  Neural circuitry is continually constructed and reconstructed in response to experience.  Consequently, while genetic predispositions influence the architecture of the dyslexic brain, there is considerable potential for functionally-significant structural modification (Shaywitz, 2003).  Therefore, it is crucial that individuals at risk for dyslexia receive effective treatment.  There is evidence that phonologically-targeted treatment can enable young individuals to sufficiently develop neural circuitry in left hemisphere posterior brain systems and to read with accuracy and fluency (Shaywitz et al., 2004).  It is also possible for the dyslexic brain to construct alternative, compensatory right hemispheric circuitry; this circuitry seems to enable accurate, but slow, reading (Shaywitz, 2003).

Who is affected by dyslexia?

Dyslexia is both prevalent and widespread.  It is the most common subtype of learning difference, with a prevalence ranging from five to ten percent (Roongpraiwan et al., 2002) to fifteen to twenty percent (Shaywitz, 2003).  It occurs in both males and females, and widely across the spectrum of intellectual ability (Shaywitz, 2003; Shaywitz et al., 1990).  Dyslexia is a global phenomena, affecting individuals across cultural, socioeconomic and linguistic boundaries (Shaywitz, 2003).  Recent research suggests that there may be an inverse relationship between the age of onset of dyslexia and the orthographic shallowness, or phonological simplicity, of a language (Kelly & Davis, 2004).  Therefore, individuals who speak languages with complex sound-letter correspondences, such as English, may present earlier with basic phonological and decoding weaknesses compared to those who speak languages with relatively simple phonological relationships, such as Finnish.

Why is early identification of dyslexia important?

It is important that dyslexia is identified as early as possible because early intervention is most effective (Lyytinen et al., 2005; Shaywitz, 2003; Torgesen, 1998).  In general, the brain is differentially plastic across the lifespan (Newport, 2002; Shaywitz, 2003). In addition, early treatment and accommodations can prevent self-esteem deficits often associated with dyslexia (Shaywitz, 2003).   

What indicators can help identify dyslexia?

Individuals with dyslexia will have a specific phonological weakness, with intact thinking and reasoning skills.  The combination of symptoms varies from case to case.  The following is a list of clues affecting spoken and written language that can signal dyslexia (taken from Shaywitz, 2003, pp. 122-127):

• Family history of dyslexia
• Slight (several month) delay in beginning to speak and in progressing to the use of phrases
• Difficulties with pronunciation of many words after five or six years of age
• Insensitivity to rhyme in early childhood (i.e. inability to recite nursery rhymes or to identify rhymes)
• Failure or delay in acquiring the ability to learn the names and sounds of the letters of the alphabet
• Confusion of words that sound alike (i.e. tornado/volcano)
• Frequent usage of imprecise words (i.e. stuff, things, etc.)
• Tendency to “talk around” a word by describing it with indirect words
• Speech littered with hesitations or pauses
• Difficulty with articulation
• Avoidance of public speaking or reading
• Use of word substitutions while reading (i.e. car for automobile)
• Difficulty reading small function words (i.e. in, on, the, that, an)
• Inability to read with appropriate speed or fluency
• Hesitant and choppy rhythm of reading, with words omitted or misspoken
• Poor spelling
• Highly variable performance on exams, with time as a strong predictor of performance
• Poor handwriting
• Reading easily disrupted in a noisy environment
• Diminished self-esteem

What should parents do if they suspect their child may be dyslexic?

If a child is showing symptoms of dyslexia, evaluation should be sought without delay.  A child can first be seen by a pediatrician, who can do an initial screening and make a referral for further evaluation if appropriate.  Speech and language therapists can carry out assessments of spoken language appropriate for young children (for an online directory of speech and language pathologists see:  If a child is of school-age, his teacher should be approached.  A school psychologist, principal, or reading specialist can also be contacted (Shaywitz, 2003).

How is dyslexia diagnosed?

Dyslexia is clinically diagnosed based upon a synthesis of information from multiple sources, including personal and family history, observations of speaking and reading, and tests of reading and language (Shaywitz, 2003).  Reading tests assess accuracy, fluency and comprehension.  An individual is considered dyslexic when she displays reading difficulties that are unexpected for her age, learning capacity and education.

What interventions are appropriate for individuals with dyslexia?

Interventions for individuals with dyslexia should include several components.  First, individuals need intensive, targeted treatment aimed at developing phonemic awareness, phonics and fluency.  In addition, they should receive instruction in vocabulary, background knowledge, and comprehension strategies. They also need to be given appropriate accommodations, such as the provision of extra time, a quiet space in which to work, recorded text, alternate testing formats, or a laptop for typing notes.  Finally, intervention should focus on the preservation of self-esteem.  Individuals must be supported and genuinely praised as they learn to read; motivation is an important ingredient of success.  They should also be encouraged to nurture the development of unaffected talents, such as athletics, music, art, science, writing, or mathematics.

Intervention at school and home should work in synchrony.  In chapters 15, 16, and 17 of Overcoming Dyslexia, Shaywitz (2003) describes a detailed program for dyslexia intervention that can be used by parents and teachers alike.  The program begins with a focus on mastering the alphabetic principle, then progresses to learning to read, and ends with developing fluency and comprehension.  Suggested activities extracted from this program are listed below.

1. Mastering the alphabetic principle

• Read stories and poems with rhyme
• Discuss stories and poems with a focus on drawing attention to sounds of language
• Practice clapping the number of syllables in words
• Play with blending syllables together (i.e. What word does rain plus bow make?  What do you get when you push the sounds, mmmm aaaa and nnnn together?)
• Compare and match sounds in different words
• Make cards with letters and match them to objects in the room that begin or end with that letter
• Play with the addition and subtraction of sounds (i.e. What would you get if you add the sound ssss to eat?  What word is made when you take the tttt from seat?) 
• Use concrete objects to represent sounds and physically move them about to create words 
• Practice reading and re-reading simple books
• Make homemade books containing familiar words and re-read them
• Make flashcards for words that do not follow a pattern (i.e. a, is, are, one, two, said, again, been, could, the, once, etc.)
• Practice writing simple words

Additional Resources:

Adams, M. J., Foorman, B. R., Lundberg, I.  & Beeler, T. (1998). Phonemic Awareness in Young Children: A Classroom Curriculum.  Paul H. Bookes, MD.

Earobics by Cognitive Concepts (

Jolly Phonics (

Yopp, H. K. (1995). Read-aloud books for developing phonemic awareness: an annotated bibliography, The Reading Teacher, 48, pp. 538-543.

2. Learning to read

• Practice sounding out words and taking them apart systematically
• Explicitly learn how letters represent sounds
• Learn about spelling
• Memorize sight words
• Learn prefixes, suffixes, and word roots
• Practice both oral and silent reading of text
• Build vocabulary through the following activities:
      -Create concept maps
      -Learn words within a theme, perhaps a theme that is an interest
      -Make use of memorable examples and illustrations
      -Create opportunities for words to be seen and used in repeated context
• Acquire an extensive general knowledge background
• Explicitly learn comprehension strategies

Additional Resources:

Adams, M. J. (1990). Beginning to Read. MIT Press, MA.

Birsh, J. R. (2005). Multisensory Teaching of Basic Language Skills.  Paul H. Brooks, MD.

Carine, D. W., Silbert, J., & Kammeenui, E. J. (1997). Instruction Reading. Prentice-Hall, NJ.

Committee on the Prevention of Reading Difficulties in Young Children, (1998). Preventing Reading Difficulties in Young Children.  National Academy Press, Washington, D.C.

3. Developing fluency and comprehension

• Practice oral reading with feedback and guidance to the student
• Practice re-reading words in related text
• Build vocabulary through the following activities:
       -Create concept maps
      -Learn words within a theme, perhaps a theme that is an interest
      -Make use of memorable examples and illustrations
      -Create opportunities for words to be seen and used in repeated context
• Establish a purpose for reading
• Identify the title and author
• Analyze the cover illustration
• Scan through the pages
• Answer the classic W’s: who, what, where, when, why
• Relate the story and events to existing knowledge and interests
• Predict future events
• Summarize main ideas
• Generate questions
• Make inferences
• Clarify difficult words or confusing concepts
• Use imagery or visualization
• Organize ideas, perhaps graphically on paper
• Retell the sequence of events

Additional Resources:

Beck, I. L., McKeown, M. G., & Kucan, L. (2002). Bringing Words to Life: Robust Vocabulary Instruction. Guilford, NY.

Beck, I. L., McKeown, M. G. & Omanson, R. C. ( 1997). The effects and uses of diverse vocabulary instructional teachinques. In M. G. McKeown and M. E. Curtis (Eds.), The Nature of Vocabulary Acquisition.  Earlbaum, NJ, pp. 147-163.     

What is the relationship of dyslexia to attention deficit hyperactivity disorder (ADHD)?

Attention deficit hyperactivity disorder (ADHD), a disorder characterized by developmentally-inappropriate inattention, hyperactivity and/or impulsivity, is often comorbid with dyslexia (Kadesjö & Gillberg, 2001).  The two disorders occur simultaneously in twelve and twenty-four percent of individuals with dyslexia (Shaywitz, 2003).  However, they do not appear to share a common cause (Doyle, 2001; Shaywitz, 2003)).

Affiliated Organizations

• International Dyslexia Association (

• International Learning Disabilities Association (

• National Center for Learning Disabilities (

• Schwab Learning (

• British Dyslexia Association (

Additional Internet Resources

• Interactive website for children with dyslexia:

• Open-source dyslexia discussion form: Learning Disability Information Exchange List LD-List (send an email to [email protected] to subscribe)

• Online magazine addressing dyslexia: Dyslexia Online Magazine,

Literature Cited

Bruck, M. Persistence of dyslexics’ phonological awareness deficits. (1992). Dev. Psychol., 28(5), pp. 874-886.

Doyle, A. E., Faraone, S. V., DuPre, E. P., Biederman, J. (2001). Separating attention deficit hyperactivity disorder and learning disabilities in girls: A familial risk analysis. Am. J. Psychiatry, 158, pp. 1666-1672.

Fisher, S. & DeFries, J. C. (2002). Developmental dyslexia: Genetic dissection of a complex cognitive trait. Nat. Rev. Neurosci., 3, pp. 767-780.

Francis, D. J., Shaywitz, S. E., Stuebing, K. K., Shaywitz, B. A. & Fletcher, J. M. (1996). Developmental lag versus deficit models of reading disability: a longitudinal, indivual growth curves analysis.  J. Educ. Psychol, 88(1), pp. 3-17.

Kadesjö, B. & Gillberg, C. (2001). The comobidity of ADHD in the general population of Swedish school-age children, J. Child Psychol. Psychiatry, 41, pp. 874-492.

Kelly, A. E. & Davis, C. (2004). Learning sciences and brain research: Second literacy and numeracy networks meeting. Madrid, Spain.

Lundberg, I. (2002). The child’s route into reading and what can go wrong. Dyslexia, 8, pp. 1-13.

Lyon, G. R., Shaywitz, S. E. & Shaywitz, B. A. (2003). A definition of dyslexia. Ann Dyslexia, 53, pp. 1-14.
Lyytinen, H., Guttorm, T. K., Huttunen, T., Paavo, J. H., Leppänen, H. T. & Vesterinen, M. (2005). Psychophysiology of developmental dyslexia: A review of findings including studies of children at risk for dyslexia. Journal of Neurolinguistics, 18(2), pp. 167-195.
Morris, R.D., Stuebing, K.K., Fletcher, J.M., Shaywitz, S.E., Lyon, G.R., Shankweiler, D.P.,  Katz, L., Francis, D.J. and Shaywitz, B.A. (1998). Subtypes of reading disability: Variability around a phonological core.  Journal of Educational Psychology, 90, 347-373.

National Center for Learning Disabilities.

Pennington, B. F. & Gilger, J. W. (1996). How is dyslexia transmitted?  Neural, cognitive, and genetic mechanisms.  In: C.H. Chase, G. D. Rosen and G. F. Sherman (Eds.), Developmental Dyslexia, York Press, MD, pp. 41-61.

Pennington, B. F. & Lefly, D. L. (2001). Early reading development in children at family risk for dyslexia. Child Dev, 72, pp. 816-833.

Ramus, F. (2004). Neurobiology of dyslexia: A reinterpretation of the data. Trends in Neuroscience, 27(12), pp. 720-726.

Ramus, F. (2003). Developmental dyslexia: Specific phonological deficit or general sensorimotor dysfunction? Current Opinion in Neurobiology, 13(2), pp. 212-218.

Ramus, F., Rosen, S., Dakin, S. C., Day, B. L., Castellote, J. M., White, S. & Frith, U.  (2003). Theories of developmental dyslexia: insights from a multiple case study of dyslexic adults. Brain, 126, pp. 841-865.  

Roongpraiwan, R., Ruanqdaraganon, N., Visudhiphan, P. & Santikul, K. (2002). Prevalence and clinical characteristics of dyslexia in primary school students. J. Med. Assoc. Thai., 85(4), pp. 1097-1103.
Rosen, Stuart. (1999). Language disorders: A problem with auditory processing? Current Biology, 9(18), pp. 698-700.
Shaywitz, B. A., Shaywitz, S. E., Blachman, B. A., Pugh, K. R., Fulbright, R. K., Skudlarski, P., Mencl, W. E., Constable, R. T., Holahan, J. M., Marchione, K. E., Fletcher, J. M., Lyon, G. R., Gore, J. C. (2004). Development of left occipito-temporal systems for skilled reading in children after a phonologically-based intervention, Biol. Psychiatry, 55, pp. 926-933.

Shaywitz, B. A., Shaywitz, S. E., Pugh, K. R., Fulbright, R. K., Mencl, W. E., Constable, R. T., Skudlarski, P., Fletcher, J. M., Reid, G. & Gore, J. C. (2001).  The neurobiology of dyslexia. Clinical Neuroscience Research, 1(4), pp. 291-299. 

Shaywitz, S. E. (2003). Overcoming Dyslexia. Random House Inc., NY.

Shaywitz, S. E., Escobar, M. D., Shaywitz, B. A., Fletcher, J. M.& Makuch, R. (1992). Evidence that dyslexia may represent the lower tail of a normal distribution of reading ability. New England Journal of Medicine, 326(3), 145-150.

Shaywitz, S. E. & Shaywitz, B. A. (2005). Dyslexia. Biological Psychiatry, 57(11), pp. 1301-1309. 

Shaywitz, S. E.,  Shaywitz, B. A., Fletcher, J. M. & Escobar, M. D. (1990). Prevalence of reading disability in boys and girls: Results of the Connecticut Longitudinal Study.  Journal of the American Medical Association, 264, pp. 998-1002. 

Stein, J. F. & Walsh, V. (2003). To see but not to read; the magnocellular theory of dyslexia. Trends Neurosci., 20(13), pp. 212-218.

Torgesen, J. K. (1998). Catch them before they fall: Identification and assessment to prevent reading failure in young children. American Educator, 22, 32-39.

Newport, E. L. (2002). Critical periods in language development. In L. Nadel (Ed.), Encyclopedia of Cognitive Science. Macmillan Publishers Ltd, London.


I would like to thank Sally Shaywitz, whose work and feedback has greatly informed this publication.