# 3.1 Tracing the transformation: how the definition of dyslexia has evolved over time

The understanding of dyslexia has evolved over time. Initially, Tansley (1957) and the World Federation of Neurology (1968) defined dyslexia as an ‘inability to read’ despite conventional instruction and adequate intelligence. Critchley and Critchley (1978) expanded this definition, describing dyslexia as a cognitive, usually genetically determined condition, not due to intellectual inadequacy or lack of socio-cultural opportunity. However, these definitions overlooked individuals with lower intelligence scores or socio-cultural disadvantages. Vellutino (1979) argued for a definition that accounted for extrinsic factors leading to reading failure and focused on subjects of average or above-average intelligence without severe neurological damage or other debilitating physical disabilities.

Despite these definitions, dyslexia lost credibility due to its requirement of academic failure for diagnosis, failure to account for the multifaceted nature of dyslexia, and marginalisation of individuals with co-occurring conditions or from disadvantaged backgrounds. In response, the Orton Dyslexia Society Research Committee drafted a more inclusive definition in 1994, characterising dyslexia as a specific language-based disorder of constitutional origin characterised by difficulties in single-word decoding. By 1996, the British Dyslexia Association broadened the definition to include difficulties with motor function, reading musical notation, organisation, and numerical skills.

In 2002, the International Dyslexia Association adopted this definition which is still used today:

> Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.

The longstanding debate over dyslexia’s legitimacy was addressed by the Rose Report, commissioned by the UK government. This report, published in June 2009, independently reviewed early reading instruction and dyslexia support and identification in England’s primary schools. You will now evaluate this report.

OpenLearn - Understanding dyslexia
Except for third party materials and otherwise, this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence, full copyright detail can be found in the acknowledgements section. Please see full copyright statement for details.