Over the past several decades, our understanding of dyslexia has advanced significantly. No longer viewed as a singular condition, dyslexia is now recognized as a heterogeneous learning disorder with multiple subtypes. One of the most extensively studied—and arguably the most challenging—is double deficit dyslexia, a term introduced by Maryanne Wolf and Patricia Bowers (1999). This subtype is marked by impairments in both phonological processing and rapid automatized naming (RAN), and it is associated with more severe and persistent reading difficulties than other forms of dyslexia.
Table of contents:
- More than a phonological deficit
- The science behind double deficit dyslexia
- Symptoms of double deficit dyslexia
- How common is double deficit dyslexia?
- Diagnosis, intervention, and prognosis
- Conclusion
More than a phonological deficit
Dyslexia has long been associated with phonological deficits, which hinder the ability to recognize and manipulate the sound structures of language. Phonological awareness is foundational for decoding words, learning to spell, and acquiring fluent reading skills. Interventions targeting this deficit—particularly systematic phonics instruction—have proven effective for many children with dyslexia.
However, researchers noted that some children continued to struggle even after robust phonological intervention. This led to the discovery of a second core deficit: rapid automatized naming, or the ability to quickly name familiar visual stimuli such as letters, numbers, or colors. RAN is not about knowing the correct word but about accessing it quickly and automatically from memory.
Wolf and Bowers (1999) proposed the double deficit hypothesis, suggesting that while some children exhibit a deficit in phonological awareness and others in RAN, a subset has both—and these children tend to experience the most severe reading impairments.
The science behind double deficit dyslexia
Studies using functional neuroimaging techniques (e.g., Shaywitz et al., 2003) have shown that individuals with double deficits display underactivation in multiple brain regions, particularly those associated with phonological decoding (left inferior frontal gyrus and temporoparietal cortex) and rapid visual processing (occipitotemporal areas). This distributed neural disruption underpins their difficulties with both accuracy and fluency.
Furthermore, research has confirmed that children with double deficits:
- Perform worse on reading fluency and accuracy tasks compared to those with single deficits (Wolf et al., 2002).
- Are less responsive to traditional phonics-based interventions alone (Torgesen et al., 2001).
- Often require more intensive, longer-duration support to make meaningful gains.
Symptoms of double deficit dyslexia
Because it impacts several core reading processes, double deficit dyslexia may present differently in each learner—but some common signs include:
- Struggles to sound out even simple words despite phonics instruction.
- Ongoing spelling difficulties, often marked by phonetic misspellings (e.g., fon for phone).
- Reads aloud slowly and unevenly, sometimes in a flat or robotic tone—even with familiar passages.
- Frequently pauses or stumbles when attempting to read or pronounce words.
- Difficulty with basic sound manipulation tasks like rhyming, breaking words into syllables, or blending sounds.
- Has trouble quickly retrieving familiar words, leading to hesitations or using incorrect substitutes.
- Tends to avoid reading because it feels frustrating, tiring, or overwhelming.
- Comprehension suffers because so much effort is spent just decoding individual words.
How common is double deficit dyslexia?
In a 2000 study, Lovett and colleagues examined 166 children aged 7 to 13 with significant reading challenges. Their goal was to determine how these children’s difficulties aligned with deficits in phonological processing, rapid naming, or both.
They analyzed data from 140 of the participants (84% of the sample). The results showed that over half (54%) of the children exhibited both a phonological and naming-speed deficit, classifying them as having a double deficit. Meanwhile, 24% had only a naming-speed deficit, and 22% had just a phonological deficit. Children with double deficits showed more profound reading impairments than those with only one type of deficit.
Despite these findings, some researchers have questioned the classification of mixed or double deficit dyslexia. Critics argue that naming-speed difficulties may not be a distinct core issue but a byproduct of phonological weaknesses. According to this perspective, naming familiar visual items quickly relies on rapid access to phonological information—which may be compromised in dyslexia due to underlying phonological processing problems (Vaessen et al., 2009).
Diagnosis, intervention, and prognosis
Formal identification typically involves standardized assessments of both phonological processing and RAN. These measures allow practitioners to distinguish between single- and double-deficit profiles, which has significant implications for targeted intervention planning.
Given its complexity, double deficit dyslexia requires multifaceted intervention strategies. Programs must simultaneously address:
- Phonological weaknesses through explicit training in phonemic awareness, decoding strategies, and orthographic mapping.
- Naming speed by incorporating repeated reading, timed naming drills, and fluency-building practices.
- Cognitive training to improve skills like working memory and attention offers the foundation to develop decoding and reading fluency.
The prognosis for double deficit dyslexia is less favorable than for other subtypes, particularly when intervention is delayed. Studies (Torgesen et al., 2001) consistently show that early intervention yields the best outcomes. When double deficits are identified early, it becomes possible to tailor instruction and reduce the severity of later academic challenges. However, since the brain is plastic throughout life, it is never too late to start.
Conclusion
Double deficit dyslexia is one of the most complex reading profiles in educational and clinical settings. It reflects the convergence of two distinct processing difficulties—each formidable independently but especially challenging in combination. Thanks to decades of research, we now understand that phonological training alone is not enough. A dual-focus approach that integrates phonics, fluency-building, automaticity, and cognitive training is critical for helping these students thrive.
Below are stories of students who received specialized help and overcame the symptoms of double deficit dyslexia:
Edublox offers cognitive training and live online tutoring to students with double deficit dyslexia. Our students are in the United States, Canada, Australia, and elsewhere. Book a free consultation to discuss your child’s learning needs.
References for Double Deficit Dyslexia: A Severe Reading Impairment
- Bowers, P. G., & Wolf, M. (1993). Theoretical links among naming speed, precise timing mechanisms and orthographic skill in dyslexia. Reading and Writing, 5(1), 69–85.
- Lovett, M. W., Steinbach, K. A., & Frijters, J. C. (2000). Remediating the core deficits of developmental reading disability: A double-deficit perspective. Journal of Learning Disabilities, 33(4), 334–358.
- Shaywitz, S. E., Shaywitz, B. A., Pugh, K. R., Fulbright, R. K., Constable, R. T., Mencl, W. E., … & Gore, J. C. (2003). The neurobiology of reading and reading disability (dyslexia). In M. S. Gazzaniga (Ed.), The cognitive neurosciences (3rd ed., pp. 865–876). MIT Press.
- Torgesen, J. K., Alexander, A. W., Wagner, R. K., Rashotte, C. A., Voeller, K. K. S., & Conway, T. (2001). Intensive remedial instruction for children with severe reading disabilities: Immediate and long-term outcomes from two instructional approaches. Journal of Learning Disabilities, 34(1), 33–58.
- Vaessen, A., Gerretsen, P., & Blomert, L. (2009). Naming problems do not reflect a second independent core deficit in dyslexia: double deficits explored. Journal of Experimental Child Psychology, 103(2), 202–221.
- Wolf, M., & Bowers, P. G. (1999). The double-deficit hypothesis for the developmental dyslexias. Journal of Educational Psychology, 91(3), 415–438.
- Wolf, M., Bowers, P. G., & Biddle, K. (2000). Naming-speed processes, timing, and reading: A conceptual review. Journal of Learning Disabilities, 33(4), 387–407.
Authored by Sue du Plessis (B.A. Hons Psychology; B.D.), an educational and reading specialist with 30+ years of experience in the learning disabilities field.
