Defining and understanding dyslexia: past, present and future.

Dyslexia is a difficulty in learning to decode (read aloud) and to spell. DSM5 classifies dyslexia as one form of neurodevelopmental disorder. Neurodevelopmental disorders are heritable, life-long conditions with early onset. For many years, research on dyslexia proceeded on the basis that it was a specific learning difficulty - specific meaning that the difficulty could not be explained in terms of obvious causes such as sensory problems or general learning difficulties (low IQ). However, the failure to find qualitative differences in reading, and phonological skills, between children with dyslexia and children with more general learning problems led this kind of 'discrepancy' definition to fall from favour. The Rose Review stated that dyslexia can occur across the IQ range and that poor decoding skills require the same kinds of intervention irrespective of IQ. In this paper, we argue that loosening the criteria for dyslexia has influenced common understanding of the condition and led to diagnostic confusion. In the longer term, the use of the term may need to change. Implications for research and practice are discussed.