What is dyslexia?
Definition of dyslexia
In February 2025, following several years of collaborative research, a new definition for dyslexia was published in the Journal of Child Psychology and Psychiatry (Carroll et al, 2025). This new definition is a summary of current and collective thinking about the nature and causes of dyslexia based on the 'Delphi' research method. This research technique involves gathering a broad range of opinions from the most experienced professionals in a field with the aim of reaching consensus on a final definition through an iterative process. The new definition succeeds the one previously used by UK-based assessors as defined in 'The Rose Report' (2009). It acknowledges the multifactorial and dynamic nature of dyslexia.
Delphi definition of dyslexia
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.
As noted by the British Dyslexia Association, 'The definition identifies the same or similar underlying cognitive indicators of dyslexia as the previous Rose (2009) definition, alongside recognition of its impact on individuals.' See: https://www.bdadyslexia.org.uk/dyslexia/about-dyslexia/what-is-dyslexia