The Official IDA Definition (2025)

“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 experiences that can impede growth in language, knowledge, written expression, and overall academic achievement. Psychological well-being and employment opportunities may also be affected. Although identification and targeted instruction are important at any age, language and literacy support during the early years of education is particularly effective” (IDA, 2025).

Let’s break this definition down piece by piece.

Why the Term “Specific Learning Disability” Matters

While much literature and research about dyslexia encourages practitioners to take a strengths-based perspective, the authors of the definition believed that it was important to keep the word disability as a part of the definition. One primary reason for this is that “specific learning disability” is the term used in the Individuals with Disabilities in Education Act (IDEA, 2004), a special education law. As such, the inclusion of this term is meant to support students with dyslexia in accessing the educational services they deserve and have the right to under the law (IDA, n.d.).

Core Characteristics: Word Reading and Spelling

Dyslexia is characterized by difficulties with word reading and/or spelling accuracy. Poor accuracy when reading words is a hallmark characteristic of dyslexia. In the new definition, the explicit inclusion of spelling difficulties as another common characteristic of dyslexia highlights how closely spelling and reading skills are linked. Students rarely present challenges with one without difficulties in the other.

The Role of Reading Speed and Orthography

When describing the word reading and spelling challenges that are typical of dyslexia, the definition clarifies that both accuracy and/or speed may be impacted, depending on the orthography. The specific writing system determines the degree to which accuracy and/or speed are impacted in dyslexia. In this case, speed refers to how automatically words are read and spelled. For example, written English does not have a one-to-one correspondence between letters and sounds. The letter combination “ow” can sound completely different in words like snow and cow. In these types of writing systems, accuracy and speed are both impacted in individuals learning to read. In contrast, other writing systems, like Spanish or Finnish, include a more consistent relationship between the sounds and letters. Readers of these languages more commonly have challenges related to speed rather than accuracy (IDA, n.d.).

Severity, Persistence, and the Need for Instruction

The authors note that these difficulties with reading and/or spelling occur along a continuum of severity. In other words, individuals with dyslexia exhibit variability in the degree to which they struggle with reading and spelling. A key marker of dyslexia is when literacy challenges persist even with instruction effective for peers. Reading is not an inherent human trait, meaning we must be directly taught in order to be able to read; we do not simply learn to read by being around books or by being read to. Without instruction in reading and spelling, anyone would struggle to learn to read. The authors emphasize that individuals with dyslexia exhibit difficulty with reading even when they are given instruction that is effective for other students, and that these challenges are not fleeting but continue over time.

A Multifactorial Cause

By using the phrase genetic, neurobiological, and environmental influences, the definition explains that there is “no single cause of dyslexia” (IDA, n.d.). Instead, dyslexia is “multifactorial,” meaning that it is the result of multiple factors combining and interacting with one another (Catts & Haynes, 2025).

Processing Difficulties and Early Language Indicators

The definition also highlights how challenges with phonological and morphological processing are often identified in dyslexia. Phonological processing can be defined as “the storage, retrieval, and awareness of speech sounds” (IDA, n.d.), and deficits in this area have often been identified in individuals with dyslexia. On the other hand, morphological processing refers to one’s awareness of, as well as one’s implicit knowledge of, meaningful parts of words, such as prefixes and suffixes (Haynes, 2025). Difficulties with morphological processing are also associated with dyslexia, especially in writing systems where the symbols used represent “chunks” of language larger than a single sound. Importantly, the definition clearly states that phonological and morphological challenges are commonly, but not universally, found in individuals with dyslexia. Thus, an individual can still be dyslexic without presenting with one or both of those deficits. Additionally, this same sentence includes mention of how early oral language weaknesses are frequently associated with later reading and writing difficulties. In other words, early delays in oral language are often seen in students who later present with word reading, spelling, and other literacy challenges (Haynes et al., 2025). 

Secondary Consequences Beyond Reading

The final sentences of the definition move beyond the characteristics and causes of dyslexia to look at dyslexia within a real-world context. The term secondary consequences refers to other difficulties that may be associated with dyslexia, including challenges with reading comprehension, writing, vocabulary development, and academic achievement, as well as negative effects on emotional well-being and quality of life (Catts & Haynes, 2025). This addition to the definition better reflects the lived experiences of persons with dyslexia and their families (IDA, n.d.). 

The Power of Early Intervention

Lastly, the definition highlights the key importance of identification and targeted instruction in remediating dyslexia, with an emphasis on instruction during the early years. In other words, while any individual can benefit from instruction regardless of their age, research has found early intervention to be the most efficacious.

A Final Note: A Key Distinction Between the 2002 and 2025 Definitions

In the 2025 IDA definition, the authors omitted the phrase: “unexpected in relation to other cognitive abilities.” Dyslexia was historically conceptualized as “reading (and spelling) difficulties that are ‘out of line’ with expectation, given age and IQ” (Snowling et al., 2020, p. 502). This idea–that the reading challenges are “unexpected”–is also known as a “discrepancy” model, meaning that a diagnosis of dyslexia required identification of a difference between a student’s reading performance and their intelligence based on cognitive testing (Tanaka & Hoeft, 2017; IDA, 2019). While a discrepancy may occur for some individuals with dyslexia, evidence of a discrepancy is no longer a requirement for diagnosis, and has not been for some time. The Diagnostic and Statistical Manual of Mental Disorders (DSM) removed this criteria in its 5th edition revisions (Tannock, n.d.), and the Individuals with Disabilities Education Act (IDEA, 2004) does not use this as a criteria when determining eligibility for special education services (Tanaka & Hoeft, 2017). The removal of the “unexpected” term from the definition reflects this shift in thinking as well as the fact that reading challenges manifest similarly in individuals with dyslexia regardless of whether their IQ scores are higher or lower than average (Haynes, et al., 2025).

References

Catts, H., & Haynes, C. (2025, November 4). Understanding dyslexia: Inside IDA’s new definition [Webinar]. AIM Institute. 

Haynes, C. (2025, November 7). IDA’s 2025 definition of dyslexia [Presentation]. Landmark Outreach.

Haynes, C.W., Malatesha Joshi, R., Catts, H., Quinonez Beltran, J.F., Lai, J. (2025). Revisiting the definition of dyslexia: An international, evidence-based update for the 21st century. https://drive.google.com/file/d/1lzQZTvJj9XIG08tN1C2sikBBmQ2TwJze/view

International Dyslexia Association (IDA). (n.d.). 2025 dyslexia definition project. Retrieved January 29, 2025, from https://dyslexiaida.org/2025-dyslexia-definition-project/

International Dyslexia Association. (2025, October 22). Definition of dyslexia. https://dyslexiaida.org/definition-of-dyslexia/

Individuals With Disabilities Education Act, 20 U.S.C. § 1400 (2004).