Is dyslexia related to intelligence?
5 minute read · updated October 28, 2026
7 sources: 2 government or law, 3 peer-reviewed research, 2 charity or professional body
No. The NHS states that dyslexia does not affect intelligence, and the UK's 2009 Rose definition says it occurs across the range of intellectual abilities.[1][2] Older approaches required a gap between IQ and reading, but a 2025 UK consensus treats that gap as a possible indicator that is neither necessary nor sufficient for a diagnosis.[2]
This page explains how definitions of dyslexia have treated intelligence over time. It is about definitions and research, not about any individual reader, and nothing here can tell you whether you are dyslexic.
Where the IQ idea came from
Early definitions built intelligence in. A 1968 definition from the World Federation of Neurology, quoted in a 2025 review, described dyslexia (in its words, "a disorder") in children who fail to attain reading, writing and spelling skills "commensurate with their intellectual abilities" despite conventional classroom experience.[2] This is the discrepancy approach: dyslexia was identified by a gap between measured IQ and reading.
The same review says researchers began to question that approach in the 1980s, and that in 1994 Stanovich and Siegel argued the underlying causes of literacy difficulties did not differ between readers with and without an IQ gap.[2] The International Dyslexia Association's 2002 definition then dropped the reference to discrepancy and used the idea of difficulties that are unexpected in relation to other abilities and teaching.[2]
Studies that tested the gap
A 2002 meta-analysis of 46 studies compared poor readers whose reading fell well below their IQ with poor readers whose reading matched their IQ. It found substantial overlap between the two groups and concluded there was little evidence supporting the IQ-discrepancy classification.[3]
A 2010 longitudinal study in Psychological Science reported that in typical readers, reading and IQ are linked as they develop over time, while in readers with dyslexia the two appear to develop more independently. The paper's title presents this as empirical evidence for a definition of dyslexia.[4]
A third study, announced by NICHD, part of the US National Institutes of Health, in November 2011, looked at 131 readers aged 7 to 16 in the Pittsburgh and San Francisco Bay areas, published in Psychological Science.[5] Using brain imaging during sound-based reading tasks, the researchers found similar results in children with dyslexia whether their IQ scores were high or low.[5]
NICHD said the results indicate that the discrepancy model is not a valid basis for allocating special reading services, and quoted the lead author, Fumiko Hoeft, saying that regardless of IQ, all children with dyslexia should be eligible for support in learning to read.[5] Many US school systems had used that model to decide who received specialized instruction.[5]
How current definitions treat IQ
| Definition | Role of IQ or intellectual ability |
|---|---|
| World Federation of Neurology, 1968 | Reading below what intellectual ability would predict[2] |
| IDA, 2002 | Reference to discrepancy removed; difficulties often unexpected relative to other abilities[2] |
| Rose, UK, 2009 | Dyslexia occurs across the range of intellectual abilities[2] |
| ICD-11 (World Health Organization) | Reading below expectations for age and intellectual ability[2] |
| DSM-5 (American Psychiatric Association) | Moves away from the ability-attainment discrepancy, focusing on unexpected attainment[2] |
| UK Delphi consensus, 2025 | A discrepancy is a useful indicator but not sufficient on its own, and should not be treated as necessary[2] |
The Delphi panel debated this point more than most. Its members did agree that support should be given to everyone with literacy difficulties, regardless of definition, and the authors write that they do not advocate using intellectual ability as an absolute measure for diagnosis or for access to services.[2]
Why ability tests still appear in assessments
An assessment may still include reasoning or ability tests. The Delphi authors say assessing intellectual abilities can be useful when diagnosing and when drawing up a support plan.[2] The UK list of suitable tests has an ability and reasoning section, and US adult evaluations commonly test cognitive ability alongside reading and spelling.[6][7] In current practice the result adds context to the reading and spelling results rather than setting a pass mark.
Quick answers
Can someone with a high IQ have dyslexia?
Yes. The Rose definition says dyslexia occurs across the range of intellectual abilities, and the 2025 Delphi paper cites studies of high-achieving adults with a dyslexic profile.[2]
Can someone with a lower IQ score have dyslexia?
Yes. A 2011 NICHD-reported study found similar results in children with dyslexia whatever their IQ, and its lead author said all children with dyslexia should be eligible for reading support.[5]
Will an adult dyslexia assessment include an IQ test?
It may. UK and US assessments often include ability or reasoning tests to give context, but the 2025 UK consensus says a gap between ability and reading is not sufficient on its own for a diagnosis.[6][2]
Does dyslexia affect intelligence?
The NHS states that it does not.[1]
Review status
Source-checked, not expert-reviewed
Drafted with AI assistance. Each factual claim was checked against the source it links to on 2026-10-28. No clinician, psychologist or dyslexia specialist has reviewed this page. See the claims register.
Sources
- [1]Dyslexia. NHS (England). Accessed 2026-10-28. Government or law
- [2]Toward a consensus on dyslexia: findings from a Delphi study. Carroll, Holden, Kirby, Thompson, Snowling and the Dyslexia Delphi Panel. Journal of Child Psychology and Psychiatry (doi:10.1111/jcpp.14123), 2025. Accessed 2026-10-28. Peer-reviewed research
- [3]Validity of IQ-discrepancy classifications of reading disabilities: a meta-analysis. Stuebing, Fletcher, LeDoux, Lyon, Shaywitz and Shaywitz. American Educational Research Journal 39(2): 469-518 (ERIC EJ654819), 2002. Accessed 2026-10-28. Peer-reviewed research
- [4]Uncoupling of reading and IQ over time: empirical evidence for a definition of dyslexia. Ferrer, Shaywitz, Holahan, Marchione and Shaywitz. Psychological Science 21(1): 93-101 (doi:10.1177/0956797609354084), 2010. Accessed 2026-10-28. Peer-reviewed research
- [5]NIH-funded study finds dyslexia not tied to IQ (news release). NICHD, 2011. Accessed 2026-10-28. Government or law
- [6]List of Suitable Tests for the Assessment of Specific Learning Difficulties (revised June 2024). SpLD Test Evaluation Committee (STEC) of SASC, 2024. Accessed 2026-10-28. Charity or professional body
- [7]Assessment of adults with LD and/or AD/HD. Kathleen Ross Kidder, LD OnLine (WETA). Accessed 2026-10-28. Charity or professional body
Related reading
- Can you have dyslexia and read well?Yes. Adults can read accurately and understand well while reading slowly or finding spelling hard. What research on students shows, and what law says.
- Is dyslexia a disability?Often yes, in law. How the ADA, the UK Equality Act 2010 and laws in Ireland, Canada and Australia treat dyslexia, and why coverage depends on your facts.
- How common is dyslexia?Published estimates range from about 5% to 20%, depending on the definition and cut-off used. The figures major organizations give, and what each counts.
- Dyslexia in adults: what the definitions sayHow the IDA and UK definitions of dyslexia differ, how dyslexia is described in adults, what co-occurs with it, and why reading difficulty has many causes.