A Practitioner’s Guide to the New Delphi Definition of Dyslexia

The SpLD Assessment Standards Committee (SASC) has now formally recognized the Delphi definition of dyslexia. This consensus-based model, developed over three years of rigorous research, marks a departure from older, more rigid frameworks. For practitioners, this is more than just a change in terminology—it is a call to evolve our diagnostic lens.

Why the Delphi Definition Matters

The Delphi definition is the result of a collaborative effort involving a diverse group of stakeholders, ensuring that the new standard is grounded in both scientific rigor and clinical reality.

While the Rose definition served its purpose, it is now 15 years old. In the intervening decade and a half, research has highlighted that dyslexia is rarely a “pure” condition existing in a vacuum. The Delphi definition addresses this by:

• Reflecting Modern Science: It acknowledges the complex, multi-factorial causal basis of dyslexia.
• Broadening the Scope: It moves beyond a heavy reliance on phonology to include other cognitive drivers.
• Lifespan Application: It is explicitly designed to be applicable across all age ranges, from early childhood through adulthood.
• Prioritizing Co-occurrence: It recognizes that overlapping conditions (like ADHD or DCD) are the rule, not the exception.

By adopting this definition, assessors ensure their practice remains “gold standard,” providing clients with reports that are not only accurate but also deeply functional.

Dissecting the Four Pillars of the Delphi Definition

The Delphi definition is structured around four critical domains: Nature, Manifestation, Impact, and Variance. Understanding these is essential for any practitioner looking to integrate the framework into their professional reports.

1. The Nature of Dyslexia: A Multi-Factorial Approach

The definition asserts that the developmental trajectory of dyslexia is shaped by an interplay of genetic and environmental influences.

Practitioner Insight: We must stop looking for a “single cause.” Dyslexia is a complex outcome. When assessing, we should consider the individual’s history, educational environment, and familial patterns as part of the broader diagnostic picture.

2. Manifestation: Beyond Phonological Awareness

For years, phonological processing was seen as the “litmus test” for dyslexia. The Delphi definition clarifies that while difficulties in phonological awareness, processing speed, and phonological memory are common, they do not tell the whole story.

The new framework explicitly acknowledges that:

• Working Memory
• Processing Speed
• Orthographic Skills (the ability to recognize and recall visual letter patterns)

All play a vital role in the manifestation of dyslexia. Assessors are now encouraged to explore how these specific cognitive domains contribute to an individual’s literacy struggles, allowing for a much more personalized profile of strengths and weaknesses.

3. Impact: Redefining Literacy Attainment

The Delphi definition shifts the focus to performance relative to context. It identifies weak literacy attainment in relation to:

• Age.
• Standard teaching and instruction.
• Level of other cognitive attainments.

Crucially, it identifies reading fluency and spelling as the primary markers of dyslexia across all languages. For the practitioner, this means that assessing the speed and automaticity of reading is just as critical as assessing decoding accuracy.

4. Variance and Co-occurrence: The Reality of the Continuum

Perhaps the most practical update is the formal recognition of the continuum. Dyslexia is not a “binary” condition (you have it or you don’t); it exists on a spectrum of severity.

Furthermore, the Delphi definition provides a clear directive to investigate co-occurrence. Dyslexia frequently overlaps with:

• ADHD (Attention Deficit Hyperactivity Disorder)
• DCD (Developmental Coordination Disorder / Dyspraxia)
• DLD (Developmental Language Disorder)
• Dyscalculia

An assessment that identifies dyslexia but ignores a co-occurring attention or language difficulty is an incomplete assessment. Practitioners must now view these overlaps as a standard part of their investigation.

Implementing the Change in Professional Practice

Transitioning to the Delphi definition requires a conscious update to how we structure our assessments and write our reports. SASC recommends the following steps for practitioners:

Update Your Citations

Assessors should formally reference the Delphi definition in their professional reports. The official citation is:

Carroll, J., Holden, C., Kirby, P., Snowling, M. J., & Thompson, P.A. (2025). The Delphi definition of dyslexia. Journal of Child Psychology and Psychiatry.

Utilize the Risks and Probabilities Framework

SASC highlights the importance of the Risks and Probabilities Assessment Practice Framework. This tool, originally published with the research preprints, provides an extended table that helps assessors structure and justify their diagnostic decisions. It acts as a bridge between the theoretical definition and the practical reality of a diagnostic session.

Focus on Secondary Consequences

The new definition encourages us to look at the “ripple effect” of dyslexia. This includes its impact on:

• Learning a second language.
• Reading comprehension.
• Mathematical reasoning (where word problems or symbolic processing are involved).
• Mental health and self-esteem.

Conclusion: A Person-Centered Future

The move to the Delphi definition represents a significant maturation of the field. It moves us away from a “check-box” mentality and toward a scientifically robust, person-centered approach.

For individuals with dyslexia, this means receiving a diagnosis that truly reflects their lived experience—one that acknowledges their struggles with fluency, their unique cognitive profile, and the very real impact of co-occurring challenges. For practitioners, it is an opportunity to sharpen our tools and ensure our expertise is aligned with the most current global consensus.