There are few concepts in education as widely accepted yet as poorly examined as dyslexia. The term carries a sense of medical authority. It suggests a clear diagnosis grounded in biology and neuroscience. In reality, the meaning of dyslexia has drifted a long way from its origins. Over many decades, we have arrived at a point where a single label is used to describe a vast range of reading difficulties that bear little resemblance to the specific phenomenon first identified. 

I want to briefly explore how this happened and why it matters.

My intention is not to dismiss the reality of reading struggles, nor to minimise the challenges children face when they cannot access written language. I want the opposite. I want us to be more honest about the complexity of these difficulties and more precise in our understanding of them. To do that, we need to revisit the history of this concept and ask whether the modern definition helps or hinders our attempts to support children.

The original meaning

The earliest descriptions of dyslexia in the late nineteenth and early twentieth centuries were not about general reading delay. They described a very small group of children who presented with unusual and distinctive visual symptoms. These children were otherwise bright and capable, yet they experienced letters that jumped, rotated, shimmered, or seemed to move on the page. Clinicians observed irregular eye movements, difficulty stabilising lines of text, and visual disorientation that could not be explained by poor teaching or low intelligence.

Dyslexia was not a spectrum. It was not a broad label. It was a rare and specific visual-perceptual disorder. Anyone reading those early case studies today would recognise immediately that the phenomenon being described is far narrower and more distinctive than the diverse difficulties now gathered under the modern label.

The great theoretical shift

The major shift began in the 1960s, when cognitive psychology started to reframe reading as a linguistic skill rather than a visual one. Researchers proposed that some children might struggle to identify or manipulate the sounds in spoken language. This phonological hypothesis grew quickly because it was measurable, testable, and theoretically tidy. Within a short time, it became the dominant explanation of reading difficulty.

The difficulty was that this new account did not match the early descriptions of dyslexia. Instead of revising the theory, many researchers reshaped the definition of dyslexia itself. Visual symptoms were not disproven. They were simply reinterpreted as peripheral or irrelevant. Over time, the phonological model became dominant. The visual-perceptual disorder that gave rise to the word dyslexia faded into the background.

As the phonological model advanced, the meaning of dyslexia shifted with it.

Expansion in the education sector

In the 1970s and 1980s, the term migrated from clinical practice into education. This was a pivotal moment. As the term entered classrooms, it broadened rapidly. Teachers and educational psychologists began using dyslexia as a label for any persistent reading difficulty that could not be explained by low general ability or poor attendance.

Working memory, rapid naming, processing speed, orthographic learning, and attention were later added as related contributors. Each addition widened the category further. By the end of the century, dyslexia had become a broad continuum of reading problems linked to a set of cognitive correlates. Two children with the same diagnosis might share very little beyond the fact that they struggled to read. A once narrow concept had become a catch all label. 

What was lost along the way

The original visual-perceptual disturbances did not vanish. Children continued to present with letters that slipped or jittered, patterns that blurred, and lines that drifted. They still describe perceptual disturbances that can make reading physically uncomfortable or disorientating. These symptoms remained real, but they no longer fitted neatly within the phonological framework. Instead of refining the definition, the field created new labels for these phenomena. Terms such as visual stress, magnocellular dysfunction, convergence insufficiency, and Irlen syndrome were introduced to house experiences that the modern model struggled to explain.

In other words, the modern concept of dyslexia does not fully account for the phenomenon that originally motivated the term.

The problem with the continuum

The modern view of dyslexia as a continuum creates a conceptual trap. If dyslexia is defined as the lower end of a reading distribution with neurological correlates, then it will always appear neurological by definition. If it is defined as a continuum, then there can never be a distinct phenotype. And dyslexia becomes a label that covers everything yet explains very little.

This does not reflect the historical reality and it may be preventing us from recognising meaningful subtypes that require different forms of intervention. It also makes it impossible to ask whether the original phenomenon was qualitatively different from general reading underperformance. The pursuit of a single explanation has produced a single label that is now stretched beyond its useful limits.

What the science actually supports

The mainstream literature today strongly supports the idea that many children with reading difficulties struggle with phonological processing. This is a real phenomenon and it matters. But this should not be conflated with the original concept of dyslexia.

The evidence for phonological difficulty explains only part of the picture. Other research programmes continue to explore visual and perceptual explanations. The magnocellular theory, championed by researchers such as John Stein, attempts to make sense of the visual instability described in early reports. The cerebellar and automatisation accounts developed by Angela Fawcett and Rod Nicolson seek to explain irregular eye movements and coordination difficulties. The neuroanatomical studies of Albert Galaburda reveal structural differences that cannot be reduced to a single cognitive deficit.

Taken together, the evidence suggests that dyslexia, as now used, is not one thing. It is a cluster of overlapping difficulties, some linguistic, some perceptual, and some developmental. The modern label hides this diversity, and in doing so, may slow our progress toward accurate diagnosis and effective support.

Why this matters for education

Educators often accept the modern definition of dyslexia without question. Teacher training rarely examines the history of the concept. Many books on dyslexia are written by individuals with little background in neuroscience, biology, research methodology, or statistics. Unsurprisingly, the field is full of assertions that are weakly supported, circular in reasoning, or based on outdated theory.

This creates several problems.

It blurs the line between reading difficulty caused by poor instruction and reading difficulty caused by a genuine neurological or perceptual difference. It also creates the illusion of diagnostic specificity when, in reality, the term is being used to cover a wide diversity of issues, some relating to teaching quality, some to language exposure, some to cognitive variation, and some to genuine perceptual disturbances. It encourages a one size fits all approach to intervention. It fosters a sense of certainty where there should be curiosity and careful inquiry. Most importantly, it stops educators from noticing the children whose difficulties fit the original visual-perceptual profile, because the label that once described these children has been stretched to cover almost everything else.

We do children no service when we allow a scientific concept to become so wide that it loses its meaning. Labels are not valuable when they are broad. They are valuable when they help us see what is specific and distinctive. At present, the term dyslexia differentiates very little.

A call for a more honest debate

I think there is value in having a clearer conversation about what dyslexia means and what it does not mean. We should not be afraid to question a concept simply because it has become part of the landscape. We should ask whether the current definition hides more than it reveals. We should be willing to revisit the early clinical descriptions and consider whether a visually grounded subtype has been neglected. We should ask whether the modern definition has become too broad to be useful. And we should ask whether the pursuit of a single explanation has led us to overlook meaningful subtypes that deserve attention. It has.

Most importantly, we should place children at the centre of the discussion rather than the label. A precise understanding of their difficulties is more valuable than a broad category that attempts to cover every possible cause of reading failure.

This is not a call to abandon the term dyslexia. It is a call to restore clarity so that we can support children with greater precision.

Appendix A. Key Figures Who Challenge the Modern Definition

John Stein

A leading advocate for a visual-perceptual account. Stein argues that differences in the magnocellular visual pathway can explain the perceptual instability described in the earliest reports of dyslexia. His work links eye movement control, motion sensitivity, and visual stability to reading.

Bruce F. Pennington

Pennington is a respected voice who challenges the idea that dyslexia has a single cause. He argues for multiple subtypes and cautions against the over dominance of the phonological model.

Angela Fawcett

Fawcett has developed the cerebellar theory of dyslexia, which proposes that difficulties in automatisation and coordination may underpin some of the perceptual features described in early dyslexia.

Rod Nicolson

Working with Fawcett, Nicolson links perceptual disturbances and motor difficulties to broader developmental processes. His work challenges the idea that dyslexia is purely linguistic.

Albert Galaburda

Galaburda has identified microstructural differences in the brains of individuals with dyslexia. His work highlights the heterogeneity of the condition and supports the idea of distinct subtypes.

Helen Irlen

Although controversial, Irlen has drawn public attention to the visual instability experienced by some readers. Her work highlights symptoms that align closely with the earliest descriptions of dyslexia.

Olaf Magnussen

Magnussen is a key contributor to research on magnocellular visual processing, which continues to inform debates about perceptual explanations of reading difficulties.

Appendix B. Suggested Reading.

Stein, J. (2019). The current status of the magnocellular theory of developmental dyslexia. Neuropsychologia, 130, 66 to 77.

Stein, J. and Walsh, V. (1997). To see but not to read. Trends in Neurosciences, 20, 147 to 152.

Pennington, B. F. (2006). From single to multiple deficit models of developmental disorders. Cognition, 101, 385 to 413.

Pennington, B. F. and Bishop, D. V. M. (2009). Relations among speech, language, and reading disorders. Annual Review of Psychology, 60, 283 to 306.

Nicolson, R. I. and Fawcett, A. J. (1990). Automaticity. Cognition, 35, 159 to 182.

Nicolson, R. I. and Fawcett, A. J. (2007). Procedural learning difficulties. Trends in Neurosciences, 30, 135 to 141.

Galaburda, A. M. and Livingstone, M. S. (1993). Evidence for a magnocellular defect in developmental dyslexia. PNAS, 90, 275 to 279.

Galaburda, A. M. (2005). Dyslexia as a molecular disorder of neuronal migration. Annals of Dyslexia, 55, 151 to 165.

Irlen, H. (2005). Reading by the colors. Square One Publishers.

Evans, B. J. W. and Allen, P. M. (2016). Controlled trials of interventions for visual stress. Ophthalmic and Physiological Optics, 36, 519 to 544.

Magnussen, S. (2014). Visual perception and dyslexia. In Visual Neuroscience. Cambridge University Press.