I often get the question from parents with children who are struggling with literacy if there is a test I can do to confirm if the child has dyslexia. There isn’t. But, the reason there isn’t is often difficult to explain, and I want to elaborate on it in this article. It comes down to what science is. 

Karl Popper developed a concept called falsifiability that has since become core to our understanding of science. Falsifiability means that for a statement to be scientifically evaluated must be capable of being proven wrong. This is the reasoning behind the statement ‘you cannot prove a negative’. For example, the statement ‘all horses have four legs’ can be easily falsified by finding a horse without four legs, but the statement ‘the Loch Ness monster exists’ cannot be falsified, you can never prove that it doesn’t exist. This however does not mean that it exists. Similarly, we cannot prove the statement ‘the sun will rise tomorrow’, yet we believe to the highest degrees of probability that it will because it has never been proven false, nor has anything indicated it won’t.

Consider these two statements:

                                THIS CHILD HAS DYSLEXIA.

                                THIS CHILD DOES NOT HAVE DYSLEXIA.

Which statement is falsifiable? In this case only the first statement can be proven wrong by testing. Which means that any given test can only tell you if a child does not have dyslexia. You cannot prove the second statement wrong, nor does failing to falsify the first statement prove it true. 

You might be thinking that if the test has failed to prove that my child does not have dyslexia then surely they must have dyslexia. This however is not the case either, since the indicators of dyslexia: poor phonemic awareness, poor spelling etc. might be caused by any number of other issues. Here’s just a small number of possible reasons a child might under-perform on a phonemic awareness test: stress, lack of sleep, AD/HD, ODD, global developmental delays, need for reading glasses or a desire to get held back in school to continue being a class with a close friend who is also being held back. So, children being tested for dyslexia who are not shown to be non-dyslexic might still be non-dyslexic but have low scores for any number of reasons.

So how can we ever diagnose dyslexia? Well, we can seek to falsify those other options. We can account for stress and sleep, test for social issues, examine medical history, compare progress in other academic areas and much more. This is what is at the heart of the scientific validity of a full psycho-education assessment, the falsification of a series of possible causes for the issues a child is facing. In the end, if every option has been falsified apart from dyslexia then the reasonable conclusion for the psychologist to arrive at is that the child is dyslexic. It is interesting to note that technically this has not been proven, much like our assumption that the sun will rise again tomorrow it has been left as the most probably theory, with nothing having been found to disprove it.

In a sense a psycho-educational assessment creates a full outline of a child by assessing every aspect, by showing both what is the case and what is not the case, rather than taking a one-directional view. This is the reason why such an assessment, to be at its fullest, requires a multidisciplinary team including psychometric, educational psychology expertise and medical expertise.

I wanted to highlight this because I’ve recently had a few parents mention single-diagnosis tests that they’ve been offered; in one case a ‘dyslexia assessment’ and another an ‘AD/HD assessment’. Both parents were curious about what the difference between such assessments entailed compared to full psycho-educational assessments, and both were surprised to hear that such assessments could not actually give them a valid diagnosis. 

Scientific validity and diagnostic strength is however only one aspect of why I so often recommend parents seek a full psycho-educational assessment. The bulk of the value that parents and educators get comes from the insight into the child’s unique strength and weakness. From the deeper understanding of who the child is, and from the recommendations for home and school that we’ve seen time and time again help make powerful improvements in the child’s life.