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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DRAFT EXPLANATION (10/28/2025, further information forthcoming)
Brief Context. The 2025 revised 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 IDAs 2002 working definition, preserving key elements while integrating insights gained over the last two decades. Below, our draft explanations are organized by sentence in the definition:
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, ICD-10). 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. The definition specifies difficulties in word reading as a core characteristic of dyslexia. The term word reading emphasizes that dyslexia involves challenges at the word-level. This includes problems with 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. Also, spelling difficulties often persist after word reading problems have been resolved and can impede written expression, notetaking, and other aspects of academic performance.
The definition also specifies that literacy difficulties can involve accuracy and/or speed, which are key components of word-level automaticity. These factors, 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. With respect to the definition’s use of “and/or” spelling, it should be noted that in some languages the term “word formation” is often a preferred term.
These difficulties occur along a continuum of severity and persist even with instruction that is effective for the individual’s peers.
The new definition is consistent with research that indicates reading and spelling difficulties are not categorical in nature, that is, show a clear division between good and poor reading/spelling. Rather literacy abilities, like many abilities, fall along a continuum of skill from good to poor with most individuals in the average range. As such, those who operationalize the definition will need to specify a point on the continuum below which would indicate dyslexia. 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 persistent 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. “Persist” is added to differentiate the difficulties from transitory ones resulting from any number of challenges that might negatively affect a person’s performance over a short period of time. The definition goes on to specify that effectiveness can be judged, at least in part, by 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 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, but neither genes or brain differences can be used to diagnose dyslexia, serve as reliable markers for the condition, or to determine an at-risk status. Crucially, 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 acknowledging the crucial role of the environment, the definition in no way suggests that environmental influences alone are a cause of dyslexia. Inclusion of throughout development emphasizes that dyslexia does not just occur in one period of human development but is a factor across the individual’s lifespan.
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 letters (or other characters), 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 word or meaningful parts of words are closely linked with the way words are spelled/written. The definition acknowledges that while phonological and morphological difficulties are common, they are not universal among all individuals who show the primary symptoms of dyslexia – significant word-reading and or spelling/word formation problems. Children with dyslexia also often have early difficulty acquiring and using spoken language. These difficulties, which can vary from mild to severe, can be indicative of an 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.
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 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 take into account the whole person.
Finally, the revised definition underscores the importance of early identification and intervention—elements 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.