The Delphi definition of dyslexia was agreed and officially published in February 2025, following three years of research and consultation with a wide range of experts. It replaces the Rose (2009) definition as the updated standard for identifying dyslexia in education and research setting. The new definition identifies similar underlying cognitive indicators of dyslexia as the previous Rose (2009) definition, and there is no need for a further assessment if diagnosed under this definition.
The Delphi Definition
Nature
• The nature and developmental trajectory of dyslexia depends on multiple genetic and environmental influences.
Manifestation
• Dyslexia is a set of processing difficulties that affect the acquisition of reading and spelling. 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.
Impact
• 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 languages and age groups, difficulties in reading and spelling fluency are a key marker of dyslexia.
Variance and co-occurrence
• Dyslexic difficulties exist on a continuum and can be experienced to various degrees of severity. Dyslexia can affect the acquisition of other skills, such as mathematics, reading comprehension or learning another language. Dyslexia frequently co-occurs with one or more other developmental difficulties, including developmental language disorder, dyscalculia, ADHD, and developmental coordination disorder.
Holden, C., Kirby, P., Snowling, M.J., Thompson, P. A., Carroll (2025) Towards a Consensus for Dyslexia Practice: Findings of a Delphi Study on Assessment and Identification, Dyslexia, 31(1), https://doi.org/10.1002/dys.1800
Further information
British Dyslexia Association (2017) What are specific learning difficulties? [online] http://www.bdadyslexia.org.uk/educator/what-are-specific-learning-difficulties
British Dyslexia Association (2017) What do I need to know as a teacher? [online]
https://www.bdadyslexia.org.uk/advice/educators/what-do-i-need-to-know
The Dyslexia Guild Code of Practice
https://dyslexiaguild.org.uk/wp-content/uploads/2025/02/The-Dyslexia-Guild-Code-of-Practice-2025-26-v2.pdf
