Dyslexia is a complex condition that can present differently in individual cases. This complexity can often lead to misinformation surrounding the process of assessment. This article explores how clinicians diagnose Dyslexia and addresses some common myths about assessments.

Female speech language pathologist asking questions and elementary school student writing answers.

Recently, I was talking with a parent about obtaining an assessment for suspected dyslexia for his first grader. That parent said that he had been told by someone who works in the field of dyslexia that “the only way to diagnose dyslexia is through a brain scan.” I was shocked. How does this mis-information get out there? I realized that I needed to write about this topic precisely because that type of mis-information does get circulated.

First—let’s be clear—we do not need brain scans to assess and diagnose dyslexia. While studies have shown promise of the potential use of fMRI in early identification of children who are at risk for learning to read, we are still far from having this tool available to diagnose dyslexia. Although the use of fMRI has also been used to show that students with dyslexia have reduced activation in the left-hemispheric occipitotemporal regions during reading and reading-related tasks when compared to peers who are good readers, we cannot yet use this tool to differentiate a typical reader from an atypical one. And, as we all know, undergoing an fMRI is very expensive.

So, until this technology is reliably developed and cost-effective, how do we assess for and diagnose dyslexia? Given that dyslexia is a language-based learning disorder, we need to first obtain a benchmark of the student’s spoken language comprehension skills. (And, to dispel another myth—IQ is not required to make a diagnosis of dyslexia.) A student’s understanding of vocabulary can serve as a proxy for verbal intelligence. A student’s spoken language comprehension scores, including receptive vocabulary, serve as a reference point from which we would predict their written language skills to fall. For the most part, a student with dyslexia will have spoken language comprehension abilities that fall within or above the average range.

The next step is to then find the reason(s) that the student is having challenges with reading and/or spelling. The majority of students identified with dyslexia have challenges with phonological processing, which refers to one’s ability to use the sounds (i.e., phonemes) of our language to develop spoken and written language. The American Speech-Language-Hearing Association (ASHA) notes that phonological processing includes “phonological awareness, phonological memory, and phonological retrieval. All three components of phonological processing are important for speech production as well as the development of spoken and written language skills.” (ASHA.org. Phonological Processing.) We can begin to assess the phonological processing skills in children as young as four years of age. Phoneme awareness, letter-sound knowledge, and alphanumeric RAN are all strong independent predictors of reading development (Clayton, et al. June 8, 2019. https://doi.org/10.1080/10888438.2019.1622546), and therefore, we can assess students who are at risk for reading success even before they enter kindergarten.

Now, that said, there are some students whose phonological processing skills score within the average range, yet, they end up struggling with learning to read and/or spell. We can see this in students who have received good intervention before receiving a diagnostic assessment for dyslexia. We know that intervention can positively impact phonological awareness skills. In some cases, we may not be able to detect a phonological weakness even if we assess early, or we can miss identifying weak skills if we wait to assess after intervention. It takes an astute diagnostician to try to tease out the factors that continue to challenge a student who has been receiving intervention. For example, a student can achieve an average score on the phonological awareness tasks of the Comprehensive Test of Phonological Processing-2 (CTOPP-2) and still be struggling greatly in reading and/or spelling. A challenge for the diagnostician is that the CTOPP-2 phonological awareness tasks do not take into account how efficient the student is in responding to a prompt, which is diagnostically informative. Evidence has suggested that struggles with speed of accessing phonological information can impact reading and spelling skills (Kilpatrick, 2015). Therefore, the diagnostician must go beyond the scores and evaluate the qualitative performance of the student as well.

If a student with good spoken language skills is struggling to learn to read (and spell), and we determine the student has average phonological processing skills, then we must dig deeper and look at orthographic processing. Orthographic knowledge is best understood as advanced letter-sound knowledge that is a result of one’s reading experience. One measure that we have found that can be informative is the Test of Orthographic Competence, particularly the subtests beginning at age eight that are timed (i.e., Letter Choice and Word Scramble). One reason it is important to assess the student’s ability under time constraints is because the need for additional time to complete activities of reading and writing can easily be accommodated in school (and work). Many successful adults with dyslexia state that while they can read and write, they continue to need more time to do so.

Finally, there are a number of students do not show deficits in either phonological processing or orthographic knowledge. Researchers have posited that students with dyslexia can have a weakness with statistical learning (Chetail, 2017; Nitzan Kligler & Yafit Gabay, 2023; van Wittleloostuijn, Boersma, Winjin, & Rispens, 2019). Statistical learning is an implicit process by which an individual learns the statistical rules and regularities in order to acquire spoken and written language skills. At present, we do not have a standardized measure to assess the statistical learning skills of students, but we can see the potential value of such a tool.

In addition to assessing the above skills, we also use standardized tests of reading to measure word-level reading of both real and nonsense words, passage-level reading, reading rate, reading fluency, and reading comprehension. Reading of nonsense words is informative in that in that they mimic words a student has never seen before, and this gives us a good picture of the students’ letter-sound understandings as well as their ability to decode or sound out words. We administer a standardized spelling measure to gain to gain a window into their phonemic awareness skills and knowledge of orthographic patterns and rules. We assess written expression skills. A measure of working memory is informative given that successful reading, spelling, and writing all require the use of working memory skills.

A comprehensive assessment for dyslexia includes analysis of the above areas and must also consider family history for dyslexia, expressive language skills, the student’ educational history, and attentional behaviors. Maybe some day in the future brain scans will be a tool that a diagnostician can use to diagnose dyslexia, but as of February 2023, they are not in our tool kits.

Joanne Marttila Pierson, Ph.D., CCC-SLP

Dr. Pierson is grateful to her colleague at 3LI, Dr. Lauren Katz, being highly skilled in the assessment, diagnosis, and treatment of individuals with dyslexia, for her careful read of and contributions to this article.