Can One Test Diagnose Dyslexia? How an Assessment Builds the Picture
Updated: Oct 28
A low spelling score, a strong reading result or a memory difficulty can raise questions about dyslexia. It is tempting to look for the one result that settles the issue. A useful assessment explains how the findings fit together and how they connect with the young person’s experience of learning.
What does the Delphi assessment research recommend?
The Delphi practice paper describes an assessment approach that combines information from different sources and considers possible explanations. These sources include relevant test results, learning history, information from home and education, and behaviour during tasks. The aim is to investigate the pattern, rather than let one isolated score decide the conclusion.
What can a test result tell us?
A standardised result describes performance on a particular task compared with the relevant reference group. The task might involve reading words, spelling, working with speech sounds or holding information briefly in mind. To understand the result, first ask what the person was required to do. Different tasks answer different questions.
For example, identifying a word correctly and reading a passage fluently are not identical demands. A strong result in one does not supply all the information about the other. Similarly, a low memory result does not itself tell you whether a reading and spelling difficulty is dyslexia.
Why does background information matter?
Imagine two learners with similar spelling difficulties on the day of assessment. One has a long history of the same concern despite targeted help; information about the other’s earlier teaching and language experience is still missing.
The current difficulty matters in both cases, but an assessor needs context before explaining it. This example illustrates the questions to investigate, not two predetermined outcomes.
You can help by describing when difficulties first became noticeable, what support has been tried and what has changed. If you do not know something, say so. A brief, honest account is more useful than trying to reconstruct an exact history or rehearse the tests beforehand.
What if the scores are uneven?
Ask the assessor to explain the differences in ordinary learning terms. Which findings help explain reading or spelling? Which describe a strength or another need? The explanation should connect the evidence, rather than assume that every low result has the same cause or that every higher result rules out difficulty.
A parent might ask: “How does this result relate to the slow written work we see at home?” or “What does this stronger result help us understand?” Those questions keep the conversation focused on the individual. A report should make the link between results and everyday learning clear.
How is this different from screening?
Screening and diagnostic assessment have different purposes. A screening result can contribute to a discussion about risk and next steps, but it is not a substitute for a full diagnostic conclusion. If you already have a school check or screening result, ask how it will be considered alongside the other evidence.
Questions to ask before booking
Ask what information will be gathered from home and education, how the assessment will address your main concerns and how the findings will be explained afterwards. Mention languages used, existing support and any practical requirements. You do not need to choose the test battery yourself or identify the expected diagnosis.
Discussing the right route
Mark Trewby offers £400 diagnostic dyslexia assessments, including a personalised report within seven working days and feedback. Online appointments cover ages 11–21 across the UK; face-to-face appointments cover ages 8–21 in Bournemouth. The separate £50 live online screening service covers ages 8–21 and does not provide a diagnosis.