Explaining the failure to learn
It seems to me that there are two interconnected reasons for the maintenance of the idea of developmental dyslexia. First, a straightforward cause is constructed to account for a child's difficulties, a cause about which all involved can feel comfortable. The cause is a glitch in brain functioning which is no one's fault, but which, like any physical dysfunction, will get in the way of development.
Failure to learn - always complex and difficult to explain satisfactorily - is thus explained simply: messy stuff to do with anxiety, emotion, motivation or language is airbrushed away. Second, an industry has been built on it, and industries find ways of promoting their products and prospering.
There's much talk about evidence-based practice nowadays, and for me the analysis of evidence about dyslexia (or at least the lack of it) ended with Gerald Coles's masterly The Learning Mystique, published in the 1980s. It's essential reading for anyone interested in this field.
It should be stressed in any debate about dyslexia that one has to distinguish between developmental and acquired dyslexia. The controversy surrounds the former, not the latter, about which no one has any uncertainties.
Professor Gary Thomas School of education University of Birmingham