The predicted prevalence of dyslexia varies depending on the precise criteria and definition used for diagnosis, but estimates generally range from 3-10%. The core element for individuals with dyslexia is a problem with word decoding, which then impacts spelling ability and reading fluency. For a long time, dyslexia has been diagnosed by the presence of on going reading difficulties, meaning that treatment and intervention is often not offered until at least two years after a child begins to show key signs. This late action is often disruptive to the child’s education, contributing to a dangerous vicious cycle where lower than expected reading ability leads to a lack of motivation in the classroom. Early identification and thus treatment of dyslexia is therefore crucial in enabling children to reach their academic potential. For this to be possible, a clear understanding of the underlying cause of dyslexia is necessary.
In the 1980s, it was discovered that dyslexic children experienced difficulties in hearing the individual sounds in words, for example difficulty in hearing that say, ‘cat’, ‘mat’ and ‘bat’ rhyme. The cognitive explanation for dyslexia is now that this limited phonological awareness (i.e. sensitivity to word sound structure) leads to difficulties in learning to read and spell. Children are taught to split a word into its component sounds, and then spell them in order, but this is not an easy task for those with dyslexia. The key question then became, why do dyslexic children have this problem?
Dyslexia has an established genetic basis, demonstrated by the observation that a male child with a dyslexic parent or sibling has a 50% chance of being dyslexic themselves. Therefore, as dyslexia is a genetic cognitive disorder, it stands to reason that there should be some underlying abnormality of the brain reflecting this genetic inheritance. As it became clear that the cerebellum is a key brain structure for both the acquisition and use of a range of cognitive skills, including ‘language dexterity’, cerebellar abnormality developed into a prime candidate for the cause of the difficulties suffered by dyslexic children.
In a study involving a panel of both dyslexic and non-dyslexic children, around 80% of the sample of dyslexic children showed clear cerebellar symptoms. Brain imaging studies of dyslexic adults also showed only 10% of the normal cerebellar activation both when carrying out a previously automatic task and when learning a new one. This suggests that dyslexic adults do not activate the cerebellum in the same way that non-dyslexic adults do when performing tasks. The final piece of evidence for the cerebellar deficit hypothesis arose from post-mortem examinations of brains from individuals with dyslexia. Abnormality, characterised by greater cell size was found in the cerebellum of dyslexic individuals. It is now thought that this cerebellar abnormality from birth leads to slight speech dysfluency, then receptive speech problems and finally deficiencies in phonological awareness at school age.
From these findings, a 30 minute screening test was put together that could be administered by a teacher in a child’s reception year. The ‘Dyslexia Early Screening Test’ is now used by over 3000 schools in the UK and can form the first stage of a screening support system. Although such screening processes are effective in identifying cognitive skills that predict literacy outcomes on a group basis, the tests do not always make accurate predictions at the individual level. The legitimacy of using such costly screening and assessment procedures must therefore be questioned.
A new approach developed in the US is the ‘response to intervention’ method. This involves monitoring the progress of a group of children during a programme of intervention instead of assessing their current skills at a given point. The children with the most need can be identified as those who do not respond as expected to effective teaching. First, all children are offered quality teaching in mainstream classes. For those who would benefit, small group catch up programmes are offered and finally, individualised intervention can be given. With this approach, the child will be offered support as soon as they begin to drop behind, rather than needing to wait to fail sufficiently so as to fulfil diagnostic criteria.
Finally, assessment undertaken by teachers at the end of the Early Years Foundation Stage could be used as a screening tool to identify children at risk of dyslexia. Findings have shown that teacher assessment at 5 years, based on on-going observations provide valid measures of attainment and can be used as a predictor of future literacy progress. Recognising that a child is showing signs of dyslexia at an early age means that a treatment plan can be put in place before the child falls behind. Effective intervention should enable the child to develop suitable coping strategies and progress academically with the appropriate support in place. Research continues into effective early intervention techniques, the future in dyslexia treatment.
References
Nicolson R, 2008, Reading and the Brain: the causes and symptoms of Dyslexia
Snowling MJ, 2012, Early identification and interventions for dyslexia: a contemporary view. Journal of Research in Special Educational Needs
Catts HW, 1991, Early Identification of Dyslexia: Evidence from a Follow-Up Study of Speech-Language Impaired Children. Annals of Dyslexia, vol. 41
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