Is there a new definition of dyslexia? Yes there Delphintitely is!
Dyslexia has never had one single, settled definition. Back in 1896, it was first described as "word blindness," a curious label for children who read nothing like their intelligence would predict. From there, the theories multiplied. Was it a visual processing issue? An IQ problem? A phonological one? For a long stretch, the official line even required a measurable gap between a child's IQ and their reading ability before a diagnosis could be given, which, let's be honest, is a wild way to decide whether a struggling reader deserves support.
Then in 2009, the UK government commissioned a review that gave us the "Rose definition," and for the past 15 years, it's been the reference point most UK assessors have worked from. It's done a solid job, but our understanding of reading difficulties has moved on a lot since then, and a new, more evidence based definition has now stepped in to take its place.
The hope isn't that this Delphi definition will end a century of debate once and for all. It's that, for the first time in a long while, experts finally have some genuine common ground to work from when it matters most: in the assessment room, with a real child in front of them.
It's called the Delphi definition of dyslexia, and here's what parents and educators need to know.
Where did it come from?
A "Delphi study" is a research method. A large panel of experts (academics, specialist teachers, educational psychologists, and people with dyslexia themselves) are asked, over several rounds, how much they agree with a series of statements. The statements are refined each round until the group reaches a collective consensus.
Researchers (who are also VIPs in the world of dyslexia research) Julia Carroll, Caroline Holden, Philip Kirby, Paul Thompson, and Margaret Snowling ran exactly this process over three years, gathering views from a wide range of stakeholders. The result: over 80% agreement on 42 statements about what dyslexia is and how it should be assessed.
What's actually different?
A few key shifts stand out:
Dyslexia is a continuum, not a box you're either in or out of. The new definition leans further into the idea that reading difficulty exists on a spectrum, rather than being a fixed category you either "have" or "don't have."
No more reliance on IQ discrepancy. Older models sometimes required a gap between a child's IQ and their reading ability before a diagnosis could be given. The Delphi consensus moves away from this approach.
A "weight of evidence" approach. Rather than one test score deciding everything, assessors are encouraged to look at several converging risk factors together; things like phonological skills, decoding ability, oral language, and family history, alongside how a child responds to teaching and intervention.
Room for co-occurring conditions. The definition acknowledges that developmental conditions like ADHD or developmental language disorder often show up alongside dyslexia, rather than treating dyslexia as an isolated condition.
Why is this a good thing?
The old, stricter cut-off models risked leaving out children who didn't quite meet the numbers but still clearly struggled and needed support. A more holistic, evidence weighted approach means assessors can build a fuller picture of a child's needs rather than relying on a single test threshold.
It also reduces the confusion caused by having several competing definitions in circulation (Rose, ICD-11, DSM-5, IDA) which is something the researchers specifically set out to address.
What does this mean going forward?
Practically speaking, if your child has already been assessed and diagnosed under an older definition, that diagnosis still stands — the researchers are clear that the underlying cognitive profile they were identifying hasn't changed. What will change over time is how new assessments are approached: less "does this one score clear the bar," more "does the overall picture, across several pieces of evidence, point to dyslexia."
The papers are currently going through peer review, so some fine tuning may still happen. But assessors are already free to use the Delphi definition now, and it's likely to become the new reference point across UK dyslexia assessment in the years ahead.
The Delphi definition is not a dramatic change, it's a much needed update that reflects 15 years of research, and one that should make assessment fairer and more accurate for the children who need it.
One to add to your shelf:
Margaret Snowling, one of the five researchers behind the Delphi study, wrote Dyslexia: A Very Short Introduction — a genuinely readable primer if you want more of the science behind everything above, straight from someone who helped shape this new definition.
