What is Dyslexia?
Dyslexia is one of the most common neurodevelopmental disorders. There have been many definitions over the past century, and debate continues as to how dyslexia should be defined. Due to ongoing research and discussion a working group of experts agreed on the following Delphi definition in February 2025:
Dyslexia is a set of processing difficulties that affect the acquisition of reading and spelling.
In dyslexia, some or all aspects of literacy attainment are weak in relation to age, standard teaching and instruction, and level of other attainments.
Across all languages, difficulties in reading fluency and spelling are key markers of dyslexia.
Dyslexic difficulties exist on a continuum and can be experienced to various degrees of severity.
The nature and developmental trajectory of dyslexia depends on multiple genetic and environmental influences.
Dyslexia can affect the acquisition of other skills, such as mathematics, reading comprehension or learning another language.
The most commonly observed cognitive impairment in dyslexia is a difficulty in phonological processing (i.e., in phonological awareness, phonological processing speed or phonological memory). However, phonological difficulties do not fully explain the variability that is observed.
Working memory, processing speed and orthographic skills can contribute to the impact of dyslexia.
Dyslexia frequently co-occurs with one or more other developmental difficulties, including developmental language disorder, dyscalculia, ADHD, and developmental coordination disorder.
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