IDA 2025 Definition of Dyslexia
“Dyslexia is a specific learning disability characterized by difficulties in word reading and/or spelling that involve accuracy, speed, or both and vary depending on the orthography. These difficulties occur along a continuum of severity and persist even with instruction that is effective for the individual’s peers. The causes of dyslexia are complex and involve combinations of genetic, neurobiological, and environmental influences that interact throughout development. Underlying difficulties with phonological and morphological processing are common but not universal, and early oral language weaknesses often foreshadow literacy challenges. Secondary consequences include reading comprehension problems and reduced reading and writing experience that can impede growth in language, knowledge, written expression, and overall academic achievement. Psychological well-being and employment opportunities also may be affected. Although identification and targeted instruction are important at any age, language and literacy support before and during the early years of education is particularly effective.”
The International Dyslexia Association (IDA) is pleased to share the 2025 Dyslexia Definition, developed through a rigorous, collaborative process to reflect the latest research and the lived experiences of individuals with dyslexia. To explore the definition in greater depth, including the scientific and community-based foundations that informed its development, visit the 2025 IDA Definition Explanation below and view the IDA Definition Presentation.
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EXPLANATION of IDA’s 2025 Updated Definition of Dyslexia
Context. The 2025 updated definition of dyslexia reflects both continuity and growth in the field’s understanding of dyslexia ’including the recognition that dyslexia occurs across languages and often impacts many aspects of the individual’s life beyond reading. It builds on IDA’s 2002 working definition, preserving key elements while integrating insights gained over the last two decades. Below, we walk readers through each sentence in the 2025 definition, explaining why we used key words and phrases.
Dyslexia is a specific learning disability characterized by difficulties in word reading and/or spelling that involve accuracy, speed, or both and vary depending on the orthography.
The definition continues to identify dyslexia as a specific learning disability—a term that is consistent with global terminology (World Health Organization). This classification also aligns with the Individuals with Disabilities Education Act (IDEA), thereby helping to ensure that individuals with dyslexia are afforded the legal rights and educational services to which they are entitled. Our Steering Committee discussed the downsides of the term “disability,” the view that dyslexia is a form of neurodiversity, as well as the important need to find and leverage strengths in all learners. In the end, we decided that the advantages of keeping the term outweigh the downsides.
The definition specifies difficulties in word reading as a core characteristic of dyslexia. The term emphasizes that dyslexia involves challenges at the word-level. This reference to word reading addresses both decoding (sounding out words using sound-symbol correspondences) and sight-word reading (recognizing words as familiar units). Reference to spelling difficulties remains in the definition because these difficulties are also a central feature of dyslexia and can impede written expression, notetaking, and other aspects of academic performance. In some languages such as Mandarin, the term “word formation” is preferred and will be included when the definition is adapted to Chinese.
The definition also specifies that literacy difficulties can involve accuracy, speed, or both. These are key components of word-level automaticity, which in turn, support text-level fluency. The phrase depending on the orthography acknowledges the understanding that languages have different orthographies, writing systems used to represent their spoken language, and the features of these systems often determine which characteristics are more prominent. For example, in languages with consistent relationships between written language units and spoken language units, difficulties with speed are more prevalent than difficulties with accuracy. The phrase or both reflects this cross-linguistic evidence that accuracy and speed difficulties may co-occur or appear separately.
These difficulties occur along a continuum of severity and persist even with instruction that is effective for the individual’s peers.
The revised definition is consistent with research that indicates that word-level literacy difficulties occur along a continuum of severity. Word reading and spelling abilities are continuously distributed, with most individuals falling within the average range and smaller percentages near the higher and lower ends of the distribution. Within this distribution, individuals with dyslexia are those who perform at the lower end of the continuum. However, there is no clear division between those with dyslexia and those who show more typical literacy abilities. As a result, determining a cut-point is ultimately the responsibility of practitioners, researchers, and policymakers. The definition does not specify that cut-point, but it does indicate that word-level literacy difficulties are the primary characteristic, and that these difficulties can vary in their severity.
To identify individuals with difficulties in word reading and/or spelling, it is essential that literacy instruction has been provided. Without instruction, most individuals would exhibit these difficulties. Ideally, instruction should be supported by research demonstrating effectiveness. However, since many instructional programs used around the world have not been rigorously studied, practices grounded in research-supported instructional principles can serve as reliable options until direct evidence becomes available. The 2025 definition reflects this understanding by continuing to specify that the individual’s word-reading and/or spelling difficulties persist even with effective instruction that is effective for the individual’s peers. The word persist is added to differentiate the difficulties from any number of transitory challenges that might negatively affect a person’s performance over a short period of time. This reference to persistence is not an endorsement of a “wait to fail” approach. Too often the identification of dyslexia has been postponed until well into the elementary school grades, far after the time that intervention is the most effective. Depending on the school’s curriculum, persistence of literacy difficulties can be observed as early as the first year of instruction and can be confirmed by means of observing the student’s response to “short-term” supplemental instruction.
The definition goes on to specify that effectiveness can be judged, at least in part, by comparison to classmates’ progress. That is, individuals with dyslexia distinguish themselves by their continued word-level literacy difficulties compared to their classmates’ expected progress. While the preferred method would be to compare students’ performance to national or state norms, this could lead to large percentages of children in underperforming schools being identified with reading disabilities. By using classroom peers’ performance as a benchmark, children who are falling behind can be identified and provided with appropriate support.
The causes of dyslexia are complex and involve combinations of genetic, neurobiological, and environmental influences that interact throughout development.
The phrase combinations of is used to underscore the research showing that there is no single cause of dyslexia and to denote that it is multifactorial in nature. Hundreds of genes have now been associated with individual differences in reading and related processes. These genes interact in complex, reciprocal ways to influence brain morphology/connectivity. Furthermore, genetic influences on brain development are more accurately characterized as differences rather than deficits, and many of these variations are also present in individuals without dyslexia. Consequently, current neuroscience does not support the existence of definitive brain-based markers for dyslexia that can be used to diagnose dyslexia or inform intervention.
The human genome does not function in isolation. Environmental, social, and mental health contexts—such as pre & postnatal conditions, adverse childhood experiences, inadequate nutrition, chronic health issues, the home literacy environment, or school anxiety—shape and interact with genetic risk. Instruction itself plays a powerful role in this interplay: when ineffective, it exacerbates challenges; when effective, it mitigates risk and supports learning.
While the revised definition acknowledges the contribution of environmental influences, it does not imply that environmental influences alone cause dyslexia. Rather, it indicates that dyslexia results from interacting factors across multiple levels of influence. Importantly, this definition challenges the current practice in some settings and locales of excluding from a dyslexia diagnosis individuals with significant environmental risk, including cultural factors, economic or environmental disadvantages, and mismatches with the language of instruction. The inclusion of the phrase throughout development emphasizes that dyslexia is not confined to a single stage of life and can often affect learning across the developmental continuum. For example, risk factors for dyslexia can impair oral language learning in the early years, reduce literacy and language learning in early grade school, impede acquisition and integration of content from research sources in middle and high school, or reduce attainment of literacy-dependent job skills in the late adolescent
Underlying difficulties with phonological and morphological processing are common but not universal, and early oral language weaknesses often foreshadow literacy challenges.
Difficulties with phonological processing, which refers to the storage, retrieval, and awareness of speech sounds, remain well-established correlates of dyslexia. Because learning to read/spell requires making connections between the sounds of spoken language and written symbols, these phonological difficulties can present significant challenges to the emerging reader/speller. Similar difficulties in processing morphemes—meaningful units that make up words—can be associated with word-level literacy difficulties. This is particularly the case in languages in which words or meaningful parts of words are closely linked with the way words are spelled/written. The phrase but not universal signals that phonological and morphological factors explain much—but not all—variations in reading/spelling seen in persons with dyslexia.
The definition’s reference to early oral language weaknesses highlights evidence linking early language delays to later challenges in word recognition, spelling, and comprehension. Children with dyslexia also often have early difficulty acquiring and using spoken language. These difficulties, which can vary from mild to severe, can indicate increased risk for dyslexia. These problems can also be a sign of more persistent oral language problems, including developmental language disorder (DLD), and should be evaluated by professionals with expertise in spoken and written language relationships. Besides language problems, a range of other difficulties can be associated with dyslexia. These include problems in working memory, speed of processing, and visual processing.
The revised definition excludes reference to other cognitive abilities, an element in the 2002 definition that often led to unsupported use of IQ-discrepancy or cognitive profile analyses to identify dyslexia. There is robust evidence that word-level literacy difficulties occur across a range of cognitive profiles, and that general intelligence bears little relationship to the nature of the word-level literacy difficulties, their underlying cognitive and neurological bases, or how students respond to intervention.
Research also indicates that dyslexia often occurs with other developmental disorders such as ADHD, developmental language disorder (DLD), and dyscalculia. While it is essential to recognize co-existing conditions during evaluation and intervention, they are distinct conditions, and as such, are not included in the revised definition of dyslexia.
Secondary consequences include reading comprehension problems and reduced reading and writing experience that can impede growth in language, knowledge, written expression, and overall academic achievement. Psychological well-being and employment opportunities also may be affected.
The definition elaborates on the secondary consequences of dyslexia to better reflect the lived experiences of persons with dyslexia and their families as well as include important insights gained from the wider dyslexia community. It continues to recognize problems in reading comprehension as a secondary consequence and adds difficulties in written expression and overall academic achievement. It also acknowledges that reduced reading and writing experiences impact vocabulary as well as other aspects of language development, particularly those found in the academic context. Also, an important addition is the impact dyslexia can have on psychological well-being, including anxiety, low self-esteem, depression, and its potential effects on career and employment opportunities later in life. Inclusion of these secondary factors acknowledges that, while reading is central to dyslexia, we need to consider the whole person. The definition neither states nor implies that all persons with dyslexia either experience or will experience these secondary consequences.
Although identification and targeted instruction are important at any age, language and literacy support before and during the early years of education is particularly effective.
Finally, the revised definition underscores the importance of early identification and support—an element not typically included in formal definitions of dyslexia. However, a growing body of research shows that providing language and literacy support and intervention before and during the earliest school years can significantly improve literacy outcomes and long-term wellbeing. Public comments overwhelmingly supported including reference to early identification and intervention in the 2025 definition. The reference to identification and targeted instruction being important at any age recognizes the continued importance of understanding strengths and specific needs of all learners with dyslexia and providing them with focused, Structured Literacy support.