The Dyslexia-ADHD Overlap: Why Evaluators Confuse the Conditions
ADHD and dyslexia share many features and frequently co-occur — an overlap that makes identifying and distinguishing the conditions a challenge – especially if both are indeed present. Here, learn why evaluators confuse ADHD and dyslexia, and how to get a clearer picture.
Dyslexia and attention deficit hyperactivity disorder (ADHD) are distinctly different. Broadly, the former is a reading disorder; the latter is associated with impaired attention and/or impulse control. So why are these conditions are often confused for one another?
In truth, considerable overlap exists between dyslexia and ADHD – from reading challenges to heritability – and both conditions frequently co-occur. ADHD and dyslexia are both linked to problems in school and with learning, but for different reasons. Ultimately, these overlapping traits complicate evaluations for ADHD and dyslexia, especially when both conditions are present. Nonetheless, a thorough evaluation that carefully considers each symptom cluster is critical to receive appropriate supports.
ADHD and Dyslexia: Similarities
ADHD and dyslexia both may bring difficulties with focusing and paying attention. For an individual with ADHD, these challenges are persistent across settings and circumstances. For someone with dyslexia, these secondary signs tend to appear when reading and language demands spike.
A student with dyslexia might tune out and look off-task – visibly similar to a student with ADHD – as they struggle to follow the teacher’s lecture or complete a reading or writing task. (Dyslexia is not just print-based, after all, but a broad language-processing issue.) What’s more, students with dyslexia often experience mental fatigue – which may manifest as inattention – as they read, write, and listen to teachers over the course of the school day.
These challenges explain why ADHD and dyslexia – individually and combined – are associated with underachievement in school. Reading is effortful, and symptoms of both conditions compound that effort and discourage many students from engaging in reading. A student who is less likely to read is also less likely to develop vocabulary and acquire knowledge across many subjects.
- Reading comprehension: Individuals with dyslexia can exhibit poor reading comprehension if they inaccurately or ineffectively read words due to poor phonological processing and fluency.But ADHD might also cause reading comprehension issues. Working memory is essential for reading, but deficits linked to ADHD make it difficult to hold information and connect it to other parts of a text. Impulsivity and inattention could also cause readers to skip over words, miss punctuation, or lose their place on the page.
- Guessing at words: Individuals with ADHD might impulsively and impatiently guess at words on the page to quickly advance their reading, but dyslexic individuals will guess because they struggle to “unlock the code” of reading. The differences come through during assessment as evaluators ask patients to break a word down or describe its sounds. (A student with dyslexia will struggle with the task.)
- Avoidance: Difficulty with tasks that require sustained mental effort — such as reading — is a DSM-5 symptom of ADHD. Similarly, someone with dyslexia will avoid reading because of inherent difficulties.
From organizing thoughts to proofreading, the writing process is complicated by both dyslexia and ADHD. Dyslexia, however, brings more spelling problems than does ADHD. (Spelling difficulties are a common feature of dyslexia.) Writing samples often help evaluators clarify the source of these challenges.
Resistance During Evaluations
A child with ADHD might struggle to comply during a dyslexia evaluation due to symptoms of inattention, impulsivity, and hyperactivity. Dyslexia could be present, but difficulty gathering meaningful data during testing will complicate the evaluator’s interpretation.
Similarly, a dyslexic child with undiagnosed ADHD might shut down or become oppositional during executive function testing and other parts of an ADHD evaluation. A lack of data will also muddle this interpretation.
There is information in resistance. More opposition during a reading activity compared to a computational activity, for instance, could indicate dyslexia. A child who struggles to focus across all activities could be showing signs of ADHD.
Heritability and Comorbidity of ADHD and Dyslexia
Separately, dyslexia and ADHD tend to run in families. The heritability of dyslexia is 40% to 60%.1For ADHD, it’s 77% to 88%.2 At the same time, 25% to 40% of individuals with ADHD also have dyslexia.3 That means individuals, families, schools, and even evaluators might inaccurately attribute signs of one condition for the other, or miss the presence of a comorbid condition entirely.
ADD and Dyslexia Evaluation: Considerations
With so much overlap between ADHD and dyslexia, an effective evaluation must consider both symptom clusters. The following elements comprise a strong, comprehensive evaluation for ADHD and dyslexia:
- An evaluator knowledgeable about ADHD and dyslexia. Look for evaluators who are members of organizations like the International Dyslexia Association (IDA), the Learning Disabilities Association (LDA), and/or CHADD. Be upfront with the evaluator – ask about their experience diagnosing ADHD and co-occurring dyslexia. If you or your child is already diagnosed with one condition, but your suspect more is going on (especially reading difficulties), don’t delay on seeking further evaluation.
- Phonological processing testing, not just reading comprehension assessments. Deficits in phonological processing, which includes the ability to distinguish sound structures in language (like the difference between “cat,” “hat,” and “mat”), are definitive markers of dyslexia and can greatly speed up evaluations. One such test is the Comprehensive Test of Phonological Processing (CTOPP), but there are others. Rapid naming, another potential indicator of dyslexia, should also be assessed.
- Testing over several sessions, especially for children exhibiting signs of inattention and impulsivity. Aim to schedule evaluations before midday, when the brain is typically at its sharpest. If you or your child take ADHD medication, the examiner will probably want you medicated on testing day, but be sure to ask ahead of time.
Dyslexia Evaluation and ADHD: Next Steps
- Self-Test: Does My Child Have Dyslexia?
- Free Download: 19 Symptoms of Adult Dyslexia
- Read: Learning Disabilities Overview — Reading, Writing & Math Disorders
The content for this article was derived, in part, from the ADDitude ADHD Experts webinar titled, “When Dyslexia and ADHD Overlap: Symptoms, Misconceptions, and Interventions [Video Replay & Podcast #403],” with Cheryl Chase, Ph.D., which was broadcast on June 1, 2022.
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1 Gialluisi, A., Andlauer, T., Mirza-Schreiber, N., Moll, K., et al. (2021). Genome-wide association study reveals new insights into the heritability and genetic correlates of developmental dyslexia. Molecular Psychiatry, 26(7), 3004–3017. https://doi.org/10.1038/s41380-020-00898-x
3 DuPaul, G. J., Gormley, M. J., & Laracy, S. D. (2013). Comorbidity of LD and ADHD: Implications of DSM-5 for assessment and treatment. Journal of Learning Disabilities, 46(1), 43–51. https://doi.org/10.1177/0022219412464351