Karina McLachlain has found a link to this very useful programme , which points out the disparities between the "common view" of dyslexia and scientific evidence. It features several of the best researchers in the field of reading and learning difficulties - Professors Keith Stanovitch, Margaret Snowling and Dorothy Bishop, and also Professor Julian (Joe) Elliott of Durham University, who approaches the topic as a straightforward but ungullible academic who wants to see propositions supported by evidence. The programme is very well worth viewing for anyone new to the subject or worried about their child.
Still, I do not believe that the evidence supports the view that there is "no such thing as dyslexia". There are some things that we do not fully understand, even with the best of evidence, and these should, I think support a definition. I suggest the following, which is as valid now as it was in the late nineteenth century, when the issue was first noticed (nobody threw rude words like "anecdotal" at those who first observed it - people recognised disciplined observations for what they might lead to in those days).
Dyslexia is a difficulty with reading and other aspects of literacy that cannot be explained by current scientific evidence.
Once a problem is pinned down by science - whether it be visual stress, slow or weak intellectual processing, clumsiness, weak awareness of sounds (whether social or medical in origin), poor teaching, very low general intelligence, aka severe general learning difficulties - then we can have a clear understanding of what we are dealing with. These difficulties and their consequences can be explained as well as described, and hence we do not need an umbrella term to cover them.
Over time, as our scientific understanding increases, our ability to select the correct teaching for the individual problem facing us will improve, and the range of issues covered by the definition will shrink. Matching teaching to learning needs should be the main focus for teacher training, and it is not.
Nevertheless, as Grace Fernald found in the 1940s, the right teaching will enable anyone to read and write within the limits of their inherent ability to understand what they are reading.
This limitation, illustrated in the work and subsequent school experience of Cushla, in Dorothy Butler's Cushla and Her Books, is not dyslexia. (Cushla, born with multiple handicaps, received from birth an intensive and inspiring introduction to books from her parents and grandparents. She responded extraordinarily well, to the extent that some people did not believe her to be handicapped. This turned out not to be true, and she never exceeded the reading expected of a seven year old. Source: personal communication from Dame Marie Clay). Cushla's difficulties were, of course, different in nature from the those of children who receive a very limited experience of language in early childhood, and so do not develop the vocabulary they need in order to succeed in school. These difficulties are social in origin, and not inherent.
Definitions, particularly of what we don't fully understand, are rarely perfect. But at least this one might rid us of our current mass-misdiagnosis, and its associated expensive "solutions". The programme is useful as an introduction to Professors Stanovitch and Snowling's emphasis on developing vocabulary and understanding as well as decoding. Many thanks to Ms McLachlain for digging it out.