Dyslexia and dyscalculia

5 min read · BoK 1B· p. 22–23

Learning objectives (3)

Define dyslexia and identify its core cognitive mechanism
Define dyscalculia and distinguish it from dyslexia
Recall prevalence figures for dyslexia

Why it matters

Dyslexia is among the most prevalent specific learning disabilities, affecting approximately 15–20% of the population to some degree. Understanding its mechanism — phonological processing, not intelligence — prevents misconceptions and informs accessible content design. Dyscalculia receives less attention but affects similar proportions of people in the context of numerical information. (BoK p. 22)

Dyslexia

Dyslexia is a specific learning disability characterized by difficulties with accurate and fluent word recognition, poor spelling, and decoding problems. It results from differences in how the brain processes the sound structure of language — not from low intelligence, poor vision, or inadequate teaching. (BoK p. 22)

Phonological processing

The core deficit in dyslexia is phonological processing — the ability to identify and manipulate the individual sound units (phonemes) of spoken language. Most people automatically connect printed letters to their corresponding sounds; people with dyslexia have difficulty making that connection efficiently.

The consequence is that reading is slow, effortful, and often inaccurate — even for people with high intelligence and good comprehension when material is read to them.

Prevalence and profile

The BoK notes that dyslexia affects approximately 15–20% of the population across a continuum of severity. Many people with dyslexia develop compensatory strategies and complete higher education; others continue to face significant reading barriers throughout life. (BoK p. 22)

Signs include:

Slow, labored reading even in adulthood.
Persistent spelling difficulties.
Difficulty reading new or complex words aloud.
Strong listening comprehension, contrasting with weaker reading comprehension.

Dyscalculia

Dyscalculia is a specific learning disability affecting number sense, arithmetic fluency, and mathematical reasoning. Like dyslexia, it is not related to overall intelligence. It affects approximately 3–7% of the population. (BoK p. 23)

Signs include:

Difficulty understanding number magnitude and quantity.
Trouble memorizing arithmetic facts.
Difficulty with multi-step calculations.
Poor sense of time and scheduling.

Dysgraphia

Dysgraphia is a specific learning disability affecting handwriting fluency and written expression. It often co-occurs with dyslexia. The physical act of forming letters is slow and effortful, independent of spelling or language competence. (BoK p. 23)

Accessibility implications

Text-to-speech allows users with dyslexia to hear content rather than read it.
Clear, simple layouts with consistent navigation reduce cognitive load.
Adjustable text spacing and fonts (sans-serif, larger size) benefit many readers with dyslexia.
Sufficient time on timed activities removes the barrier of slow reading pace.
Plain language helps users with dyscalculia avoid getting lost in number-heavy content.

Real-world example

An insurance company’s online application includes dense policy terms in 8-point print and a 10-minute session timer. A user with dyslexia and average intelligence reads slowly and cannot complete the form before the timer expires. Adding a text-to-speech option, extending the session timer, and rewriting the policy text in plain language removes barriers without reducing the content’s legal substance.

Key terms

Dyslexia: A specific learning disability affecting reading fluency and decoding, rooted in phonological processing difficulties, not intelligence. (BoK p. 22)
Phonological processing: The ability to identify and manipulate the sound units (phonemes) of language — the core deficit in dyslexia. (BoK p. 22)
Dyscalculia: A specific learning disability affecting number sense, arithmetic, and mathematical reasoning. (BoK p. 23)
Dysgraphia: A specific learning disability affecting handwriting fluency and written expression, often co-occurring with dyslexia. (BoK p. 23)
Learning disability: In the US context, a specific neurological condition affecting one or more academic skills despite adequate intelligence and instruction. (BoK p. 22)

Check yourself

A graduate student with dyslexia is highly articulate in conversation, excels in verbal reasoning tests, and earns top marks in oral presentations. However, she reads slowly, misspells words she knows orally, and struggles with new technical terms in print. Which feature of dyslexia does the BoK identify that explains this profile?

Dyslexia is a vision problem that causes letters to appear reversed
Dyslexia is a phonological processing disorder that affects reading mechanics independently of intelligence or oral language ability
Dyslexia is a form of intellectual disability affecting all academic skills equally
Dyslexia is caused by low intelligence and limits overall academic performance

.cy-island-wrapper { display: none; }JavaScript is required for the interactive quiz. Here are the questions for reference:

a) Dyslexia is a vision problem that causes letters to appear reversed
b) Dyslexia is caused by low intelligence and limits overall academic performance
c) Dyslexia is a phonological processing disorder that affects reading mechanics independently of intelligence or oral language ability — correct answer
d) Dyslexia is a form of intellectual disability affecting all academic skills equally

Explanation: Dyslexia is defined by a specific deficit in phonological processing — connecting printed symbols to speech sounds. Because the deficit is in reading mechanics, not in comprehension, reasoning, or oral language, people with dyslexia often show the exact profile described: strong verbal and reasoning ability combined with slow, effortful reading and spelling difficulties (BoK p. 22).

According to the BoK, approximately what percentage of the population has dyslexia to some degree?

a) 1–2%
b) 5–7%
c) 15–20% — correct answer
d) 40–50%

Explanation: The BoK states that dyslexia affects approximately 15–20% of the population along a continuum of severity. Most people with dyslexia are at the mild end of the continuum and develop compensatory strategies. The high prevalence underscores why reading accessibility — text-to-speech, plain language, and flexible text display — has broad impact (BoK p. 22).

A user with dyscalculia is reviewing an insurance policy that presents deductibles, premiums, and co-pays as raw numbers without contextual explanation. Which accessibility measure would most directly reduce the barrier created by dyscalculia in this context?

a) Text-to-speech narration of the numbers
b) Increasing the font size of the numerical content
c) Expressing numerical information with plain-language explanations and contextual comparisons — correct answer
d) Providing captions for any audio explanation of the numbers

Explanation: Dyscalculia creates difficulty understanding numerical information — not just reading it. The accessible solution is to supplement or replace raw numbers with plain-language explanations, contextual framing, and visual comparisons that support number sense. This is consistent with the BoK's function-based approach: address the functional barrier (difficulty reasoning with numbers) rather than just the modality (BoK p. 23).

Sources

BoK references

Section 1B — IAAP CPACC Body of Knowledge v4.0 (Oct 2023), p. 22–23