assessment, suggesting that boys with reading difficulties come to the notice of teachers more frequently than girls, perhaps because they compensate less well or behave more disruptively. The term ‘dyslexia’ is often used as a synonym for specific reading difficulties. However, there are a number of problems with this practice; a child can fulfil the criteria for specific learning difficulties for several reasons, perhaps because of absence from school, because of poor engagement with learning or as a consequence of poor teaching. A further limitation that follows from defining a reading disorder in this way is that it tells us nothing about the manifestations of dyslexia in the preschool years or in adulthood when reading difficulties may be largely overcome but spelling problems persist.
Specific learning difficulties Margaret J Snowling
Specific learning difficulties (SLD) is a term commonly used to describe the ‘unexpected’ problems that some children experience in the academic arena. These children’s difficulties are out of line with what might be ‘expected’ given their age and general cognitive ability. In contrast, the term learning disabilities (mental retardation in the USA) is used to describe learning problems that occur in the context of more global delays in cognitive development, signalled by low IQ. To describe a child as having a ‘specific learning difficulty’ carries no implication about the nature or aetiology of his or her problems. Rather SLD is a statistical definition that should be regarded as the starting point of a more detailed assessment of the child’s strengths and difficulties. Indeed, there are many different kinds of specific learning difficulty; the present paper focuses on reading and spelling difficulties (dyslexia and dysgraphia), arithmetic problems (dyscalculia) and problems of motor coordination (dyspraxia). The syndrome of ‘nonverbal learning disabilities’ is also discussed.
Nature and causes of dyslexia Despite continuing debate as to the precise criteria for the diagnosis of dyslexia, advances have been made in the understanding of its biological substrate. Findings of gene markers for dyslexia on chromosomes 6, 15 and 18 have been replicated in several independent studies, and differences in brain structure and function, particularly in left hemisphere temporal regions, have been observed when people with dyslexia have been compared with normal readers.2 At the cognitive level, there is a consensus that dyslexic people show a phonological (speech)-processing deficit. The manifestation of this deficit at the behavioural level changes as the child develops, as shown in Figure 1. Evidence is also emerging that interventions can bring about changes in activation to the brain circuitry involved in reading in children with dyslexia.3 It has been suggested that dyslexic difficulties are the result of low-level visual impairments. However, reports of raised thresholds for contrast sensitivity and visual motion detection in dyslexia, or problems with ocular motor control, have not been consistently replicated. More recent research suggests there may be higher-level problems in the allocation of visual attention in at least some individuals. Another influential hypothesis is that the phonological deficit in dyslexia can be traced to impairments of basic auditory processing mechanisms; however, although there is evidence of an association between auditory and phonological processing deficits in some individuals, it is far from clear that the relationship is causal.4 An alternative view traces the phonological deficits observed in dyslexia to a language-based difficulty in the mental representation of the spoken structures of words.5 These difficulties compromise the child’s ability to learn alphabetic mappings between sounds and letters for reading and for spelling. Increasing evidence suggests that English orthography, being highly inconsistent in these mappings, may aggravate dyslexia; dyslexic readers of German, Italian and other transparent languages display phonological deficits but have more accurate (but slow) reading and spelling. Figure 2 presents a framework adapted from Morton and Frith to illustrate the role of the cognitive deficit as the mediator of the brain–behaviour relationships and environmental interactions in dyslexia.6
Dyslexia The ‘discrepancy’ definition It has become conventional in clinical practice to distinguish children who have specific reading difficulties from children who have reading difficulties in the context of more general learning problems. A child is deemed to have a specific problem with reading if their reading attainment is significantly below that predicted from their mental age on the basis of the correlation between reading and IQ in the same population. Such children show a discrepancy between expected and actual attainment. Prevalence – the prevalence of specific reading difficulties depends on the specific cut-off point taken as indicative of reading disability. Recent epidemiological data from a longitudinal study of Connecticut children reported prevalence rates of between 5.4% and 7% depending on age.1 In contrast to earlier studies that reported 3–4 males to every female affected, this study reported a more even sex distribution. However, school records showed that more boys than girls in the sample had been referred for
Treatment There is now a sizeable evidence base showing that the most effective interventions for dyslexia combine training in oral phonological awareness with highly structured reading practice using text, and linking phonological units to sounds through writing. Children at risk of reading failure need individualized intervention
Margaret J Snowling holds a Personal Chair in Psychology at the University of York, UK, where she directs the Centre for Reading and Language. After completing a doctorate on developmental dyslexia at the Developmental Psychology Unit in London, she subsequently qualified as a clinical psychologist. Her research focuses on the interface of spoken and written language.
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Manifestation of dyslexia across the lifespan Pre-school
Early school years
Middle school years
Delayed speech Immature sentence formation Poor expressive language relative to comprehension Poor rhyming skills
Poor memory for verbal instructions Difficulties with common sequences (e.g. days of the week) Poor letter knowledge Poor phonological awareness
Subtle speech problems (e.g. on polysyllabic words) Word-finding difficulties Difficulty learning tables and number facts Slow reading
Poor verbal memory Word-finding difficulties/make malapropisms Slow reading Slow speed of writing Poor proof-reading skills
Little interest in or
Poor phonics (word-attack skills)
Poor decoding skills when
Difficulty committing ideas to paper
knowledge of letters
even if reasonable sight vocabulary
faced with new words
Poor organization of written work
Problems with copying
Slow at copying
Normal development of number skills Adopting a developmental framework provides a useful way of considering children’s problems with arithmetic.8 By the age of 6, most children can use a ‘counting on’ strategy to add, sometimes using their fingers to monitor this process. Later, as they learn number facts, they can begin to retrieve these automatically. Importantly, the development in long-term memory of an association between the problem integers (e.g. 3+4) and the answer that is generated (7) requires practice in the execution of basic computations. With each execution, the probability of direct retrieval of that number fact increases. It follows that children who have difficulty with basic computation will have difficulty establishing a database of number knowledge, and hence, in becoming numerate. Moreover, since more advanced mathematics builds on a foundation of basic arithmetic skills, child who fall behind in the early stages have difficulty understanding and using more advanced concepts. They also often suffer anxiety about mathematics.
from school entry to prevent them falling behind their peers, and support in mainstream classrooms to ensure they can properly access the curriculum.7
Dysgraphia Spelling skills in dyslexia The spelling skills of dyslexic children are almost always impaired; moreover, dyslexic children often commit dysphonetic spelling errors that are phonetically unacceptable (e.g. geography > georafy). A second source of spelling difficulty is poor knowledge of orthographic conventions. Since English is an opaque orthography in which spelling–sound correspondences are not consistent, phonetic spelling errors are frequently observed (e.g. biscuit > biskit; chaos > kaos). Specific spelling disabilities Spelling problems can sometimes be experienced in children who are not dyslexic. Such children who read well but have specific spelling problems have been described as dysgraphic. Dysgraphic children tend to spell phonetically and they have difficulty selecting the correct spelling from two plausible alternatives (e.g. successful/succesful; necessary/necessery). It has been proposed that dysgraphia may arise as the consequence of a ‘hidden’ reading problem; indeed, people with poor spelling do not read in a detailed way. Typically, they rely heavily on context, and they are bad at proof-reading. There is also some evidence that such people have subtle visual memory deficits.
Nature and causes of dyscalculia Children with dyscalculia typically show the following characteristics: • use the same strategies as younger children for calculating but are error-prone • slow at counting and at calculating • difficulty retrieving number facts • do not know their tables • poor at monitoring their counting and at detecting computational errors • problems switching between different strategies when completing mathematical problems. The cognitive causes of dyscalculia are not as extensively researched as those of dyslexia. Theoretically, there are grounds for distinguishing a non-verbal magnitude system (thought to be controlled by right hemisphere processes) from a verbal number system (putatively in the left hemisphere). In line with this view, some children have difficulties in learning mathematical concepts, while others have selective deficits of the calculation system. Some researchers view working memory difficulties as candidate causes of arithmetic problems, since numbers have to be held in short-term memory during the process of mental calculation,
Dyscalculia The term dyscalculia is used to refer to specific difficulties with numeracy skills. Dyscalculia is characterized by a problem in learning number facts and hence with arithmetic. The incidence of underachievement in arithmetic is less well documented than for reading. Figures of around 6% have been reported, but these figures do not take into account the common comorbidity with reading problems. In fact, although ‘pure’ dyscalculia is rare, there is no strong evidence that it differs in nature from dyscalculia with dyslexia.
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impairment or autism. In fact, many children with specific language impairment have dyspraxic difficulties that are equivalent in magnitude to those of children with DCD. There is little agreement among professionals about terminology or about assessment criteria for DCD.10 Its symptoms can vary considerably and may include gross motor difficulties, such as problems running, hopping, jumping, catching a ball and balancing, and fine motor difficulties including a lack of manual dexterity, difficulty in doing up buttons and laces, in dressing and in using eating utensils. Speech–motor skills can be affected and problems of pencil control are widespread. A mistaken view is that dyspraxic children grow out of their clumsiness; follow-up studies have shown that such children remain less physically competent throughout adolescence and the difficulties they have at secondary school include problems with handwriting and the presentation of work, and difficulties in science, art, design and technology. Indeed, there is some evidence that they do less well academically than their IQs predict.
Causal modelling framework for brain–behaviour relationships in dyslexia Genes
Phonological deficit COGNITION
Causes of and treatments for dyspraxia Considering the heterogeneity of dyspraxia, it is unlikely to have a unitary cause. It is well established that dyspraxic children have visuospatial difficulties, but some cognitive theories of DCD have emphasized problems of kinaesthetic sensitivity, cross-modal transfer or timing. The lack of consensus has made it difficult to make progress in the evaluation of treatments. Children with coordination difficulties need to have a comprehensive assessment of their gross and fine motor skills and of how their ‘clumsiness’ affects the completion of everyday tasks. Their educational attainments should also be assessed so that a management plan, usually involving a physiotherapist or occupational therapist, as well as a teacher, can be devised.
Poor phonological awareness
The right-hand side of the figure shows three different levels of explanation. At the biological level of description, there are genetic and brain theories of dyslexia. The symptoms of dyslexia can be seen at the level of behaviour. The intermediate level of cognition mediates relationships between biology and behaviour, and in dyslexia a phonological deficit is inferred. The left-hand side of the figure shows that at every level, there are interactions with the environment. A specific example is that the writing system of a language (orthography) plays a role in modifying the symptoms of dyslexia.
Comorbidity of specific learning difficulties It is very common for specific learning difficulties to co-occur both with one another and with other disorders. For example, many children with dyslexia also have motor difficulties or ADHD. Theoretical accounts of specific developmental disorders that posit core cognitive deficits can provide a useful way of thinking about specific learning difficulties without the need to classify them discretely. Thus, knowing that the core deficit in dyslexia is a phonological deficit explains why reading difficulties are experienced by many children with oral language difficulties.11 As yet, cognitive models of dyscalculia and dyspraxia are not well specified. In the absence of these, an overarching syndrome of non-verbal learning difficulties (NVLD) has been proposed to explain the frequent co-occurrence of such problems, together with dysgraphia.12 In the Nordic countries, the term DAMP (disorders of attention and motor perception) has been preferred to describe children of normal intelligence with dyspraxic tendencies and ADHD; however the syndrome has not been fully validated.13 While there is not agreement about the symptoms of non-verbal learning difficulties (Figure 3), it is generally believed that these children have deficiencies in visuospatial organization and nonverbal integration, and they usually gain higher scores on Verbal than Performance IQ tests. Although described as a non-verbal syndrome, many such children have reading comprehension difficulties, mild speech–language impairments and pragmatic
(Adapted from Morton and Frith, 1995)6 2
and a spatial representation of the problem to be solved can be helpful in some forms of problem-solving. One of the reasons that many dyslexic children are also dyscalculic is because they have verbal short-term memory difficulties that compromise arithmetic skill.9 Importantly, a range of control processes is also involved in selecting appropriate algorithms and in the monitoring of performance; for example, checking that the solution to a problem is within the estimated range.
Dyspraxia The nature of dyspraxia The term ‘dyspraxia’ is commonly used to describe problems of motor coordination that can occur in isolation in otherwise normal children (developmental coordination disorder, DCD) or that co-occur with other developmental disorders such as language
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3 Shaywitz B A, Shaywitz S E, Blachman B A et al. Development of left occipitotemporal systems for skilled reading in children after a phonologically-based intervention. Biological Psychiatry 2004; 55: 926–33. 4 Ramus F, Rosen S, Dakin S C et al. Theories of developmental dyslexia: insights from a multiple case study of dyslexic adults. Brain 2003; 126: 1–25. 5 Snowling M J. Dyslexia. Second edition. Oxford: Blackwell, 2000. 6 Morton J, Frith U. Causal modelling: a structural approach to developmental psychopathology. In: Cicchetti D, Cohen D, eds. Manual of developmental psychopathology. New York: Wiley, 1995. 7 Snowling M J, Stackhouse J. Dyslexia, speech & language: a practitioner’s handbook. Second Edition. London: Whurr, 2005. 8 Butterworth, B. The development of arithmetical abilities. J Child Psychol Psychiatry 2005; 46: 3–18. 9 Hulme C, Roodenrys S. Practitioner review: Verbal working memory development and its disorders. J Child Psychol Psychiatry 1995; 36: 373–98. 10 Sugden D A, Chambers M. Children with developmental coordination disorder. Chichester: John Wiley and Sons, 2005. 11 Bishop D V M, Snowling M J. Developmental dyslexia and specific language impairment: same or different? Psychological Bulletin 2004; 130: 858–88. 12 Rourke B P, ed. Syndrome of nonverbal learning disabilities: neurodevelopmental manifestations. New York: Guildford Press Inc., 1995. 13 Gillberg C. Clinical Child Neuropsychiatry. Cambridge: Cambridge University Press, 1999. 14 Bishop D V M, Baird G. Parent and teacher report of pragmatic aspects of communication: use of the Children’s Communication Checklist in a clinical setting. Dev Med Child Neurol 2001; 43: 809–18. 15 Klin A, Volkmar F R, Sparrow S S, Cicchetti D V, Rourke B P. Validity and neuropsychological characterization of Asperger Syndrome: Convergence with Nonverbal Learning Disabilities Syndrome. J Child Psychol Psychiatry 1995; 36: 7: 1127–40.
Clinical characteristics of non-verbal learning difficulties Early years Language development Motor development Attention
Slow to develop but catches up Poor gross and fine motor skills except when skill is well practised Hyperactive when young becoming hypoactive
Primary school years Visuo-perceptual and spatial problems Reading (word level)
Good or phonetic
Later school years and adolescence Pragmatic language skills
Social skills and peer relationships Socio-emotional adjustment
(Source: Rourke, 1995; Klin et al., 1995)12,15
deficits.14 Indeed, the high incidence of social and pragmatic impairments in NVLD suggests a continuum of this disorder with Asperger’s syndrome at the severe end.15
Conclusion The term specific learning difficulties is used widely in educational practice to describe problems in learning that are out of line with expectation given general cognitive ability. We have seen that the term can be an umbrella definition for a range of disorders, each with different core features. A problem for clinicians is that the behavioural manifestations of these disorders vary across the lifespan and differ where there are associated comorbidities. It is wise, therefore, for clinicians to take careful case-histories from patients presenting with a SLD; information about family history, speech, language and motor development can provide important pointers to the causes of the difficulties these children have with learning. Comprehensive management programmes should also take account of current attainments in reading, spelling, number skills and written work, relative to age and ability.
Practice points • Specific learning difficulties (SLD) is an umbrella term; they can take many forms • Dyslexia is a specific reading difficulty associated with phonological (speech) difficulties • Dysgraphia is a specific spelling difficulty that can occur with dyslexia or alone • Dyscalculia is a specific difficulty with numeracy associated either with spatial difficulties or with verbal short-term memory problems • Dyspraxia refers to problems of motor coordination and frequently co-occurs with language disorders • There are frequent comorbidities between developmental cognitive disorders • SLD is only the starting point for the assessment and management of children with developmental disorders of learning
REFERENCES 1 Shaywitz S E, Escobar M D, Shaywitz B A, Fletcher J M, Makugh R. Evidence that dyslexia may represent the lower tail of a normal distribution of reading ability. N Engl J Med 1992; 326: 145–50. 2 Démonet J-F, Taylor M J, Chaix Y. Developmental dyslexia. Lancet 2004; 363: 1451–60.
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