Why a New Definition of Dyslexia Matters

When people hear that the definition of dyslexia has changed, their first reaction is often to ask, “Well, what changed?” In the case of dyslexia, the most significant change was removing language that had long been used to require a gap between IQ and expected reading performance before students could qualify for services.

I think, however, the more important question is, “Why was it changed?” And from my perspective, the revision accomplishes two important goals.

First, it reflects what we’ve learned from more than two decades of additional research. As our understanding evolves, our definitions should evolve too.

Second, it addresses some of the misconceptions that have emerged from the way the previous definition was interpreted. This is particularly important because most people don’t read lengthy research papers or technical explanations. They read a definition, hear a phrase repeated, and understandably begin to build conclusions around it.

One example is the phrase “often unexpected in relation to other cognitive abilities,” which appeared in the previous definition. Over time, that language became closely associated with identification approaches that compare a student’s reading achievement to measures of cognitive ability or IQ. The logic was that a student needed to demonstrate an “unexpected” gap between intelligence and reading performance in order to be considered dyslexic.

The challenge is that decades of research have shown those approaches do not create educationally meaningful groups of students.

If two students demonstrate similar reading difficulties, the fact that one has a higher IQ score than the other does not mean they require fundamentally different reading instruction. Yet discrepancy-based models have sometimes led schools to focus on the gap itself rather than the student’s reading needs.

The revised definition moves away from that idea. Instead, it places greater emphasis on the persistence of reading and spelling difficulties despite effective instruction. For educators, that’s an especially significant shift.

The question becomes less about whether a student’s reading difficulties are “unexpected” and more about whether the student is responding to instruction at the rate we would expect. If a student is struggling with word reading or spelling, we should provide intervention. If that intervention is evidence-based and delivered effectively, we should monitor progress. And if the student continues to make significantly less progress than peers receiving the same support, that’s important information that tells us something about the intensity of support that student may need.

I also appreciate that the revised definition clarifies some common misunderstandings about dyslexia itself. For example, people often latch onto highly technical terms and assume they represent the entire condition. And, historically, discussions have focused heavily on phonological processing—or the ability to use sound to process spoken or written language. (While difficulties in phonological processing are common among students with dyslexia, they are not universal.) The revised definition reflects a broader understanding of reading development and acknowledges that reading and spelling difficulties can present in different ways—including through challenges with orthographic processing, which is the ability to connect letters to their corresponding sounds and spellings.

Most importantly, the revised definition keeps the focus where it belongs: on students.

For district leaders and educators, the practical implications are not especially complicated. When students demonstrate difficulties with reading and spelling, identify those needs early, provide intervention, monitor progress carefully, and intensify support when necessary. In other words, focus less on fitting students into a predetermined profile, and more on understanding how they respond to instruction.

Because ultimately, the goal is to make sure students receive the support they need to become successful readers.

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