Pattern of Strengths and Weaknesses: How This Model Identifies Dyslexia When IQ Tests Fail

For decades, getting a child identified as having a Specific Learning Disability required demonstrating a "severe discrepancy" between their IQ score and their academic achievement. In theory, this sounded reasonable — a child reading well below their cognitive potential clearly had a learning disability. In practice, it created the "wait to fail" problem: most young children, even severely dyslexic ones, did not yet show a large enough statistical gap between their intelligence and their reading scores to qualify. Schools had to watch a child fall progressively further behind for two or three years before the discrepancy appeared.

The 2004 reauthorisation of IDEA permitted alternatives to the discrepancy model. The most clinically sophisticated of these alternatives is the Pattern of Strengths and Weaknesses (PSW) model — and for parents advocating for students with dyslexia, understanding how it works is essential.

What the PSW Model Actually Looks Like

The PSW model does not ask "is there a gap between IQ and achievement?" It asks a different, more precise question: "Is there a specific pattern of neurological processing strengths and weaknesses that is causing this student's unexpected academic difficulty?"

In dyslexia, that pattern is highly consistent and well-documented:

Typical cognitive strengths:

• Verbal Comprehension (understanding language, vocabulary, reasoning with words)
• Visual Spatial reasoning (often strong in many dyslexic students)
• General knowledge and conceptual thinking

Typical cognitive weaknesses (the processing deficits):

• Phonological Awareness — the ability to identify, segment, blend, and manipulate individual sounds in spoken language
• Phonological Memory — holding sound sequences in working memory long enough to decode a word
• Rapid Automatised Naming (RAN) — the speed with which the brain retrieves the phonological labels for familiar symbols (letters, numbers, colors, objects)
• Processing Speed — the speed of routine cognitive operations, especially those involving symbol processing

The academic consequence:

• Below-expectation word reading accuracy and fluency
• Below-expectation pseudoword decoding (nonsense word reading, which isolates phonetic decoding from sight-word memory)
• Spelling difficulties

The PSW identification is made when: (1) the cognitive processing weaknesses are statistically significant and consistent with dyslexia's neurological profile, (2) those specific processing weaknesses are logically connected to the academic weaknesses, and (3) the academic weaknesses are unexpected given the student's overall cognitive ability.

The Tests That Make Up a PSW Assessment

A proper PSW-informed evaluation must independently measure all three components: cognitive ability, specific processing, and academic achievement.

Cognitive ability: The WISC-V (Wechsler Intelligence Scale for Children, Fifth Edition) is the most widely used instrument. The PSW analysis relies on examining the pattern within the WISC-V profile — specifically comparing the Verbal Comprehension Index (VCI) with the Working Memory Index (WMI) and Processing Speed Index (PSI). A student with high VCI and significantly depressed WMI and PSI scores has a within-battery cognitive pattern consistent with dyslexia.

Phonological processing: The CTOPP-2 (Comprehensive Test of Phonological Processing, Second Edition) is the gold standard instrument. It directly measures:

• Phonological Awareness — subtests include Elision (removing sounds from words) and Blending Words (combining sounds into words)
• Phonological Memory — measured through Nonword Repetition (repeating nonsense words of increasing length)
• Rapid Symbolic Naming — RAN for letters and digits

CTOPP-2 scores below the 16th percentile (standard score below 85) on phonological awareness or RAN are significant findings. Scores below the 10th percentile (standard score below 80) represent a substantial deficit.

Academic achievement: The WIAT-4 (Wechsler Individual Achievement Test, Fourth Edition) or Woodcock-Johnson IV Tests of Achievement are standard. Key subtests for dyslexia include:

• Pseudoword Decoding — reading nonsense words, which removes sight-word memorisation from the equation and reveals pure phonetic decoding ability
• Word Reading — accuracy on real words
• Orthographic Fluency — speed of recognising correct spelling patterns
• Spelling — encoding accuracy

The WIAT-4 includes a "Dyslexia Index" composite that summarises the reading and spelling subtests most sensitive to dyslexia.

Why PSW Is Superior to the Discrepancy Model for Dyslexia

The discrepancy model fails dyslexic students in two specific populations:

Young students. A first-grader with severe dyslexia may have an average reading score because reading expectations in first grade are simply not demanding enough to reveal the gap yet. The discrepancy does not appear until third or fourth grade. The PSW model can identify the dyslexia profile — severe phonological processing deficits alongside intact verbal reasoning — as early as kindergarten or first grade, enabling intervention during the critical neuroplastic window.

Compensating students. A high-ability student with dyslexia may achieve average reading comprehension scores by using their superior reasoning to contextualise unfamiliar words. Their pseudoword decoding and phonological awareness scores reveal a severe phonological deficit that their intelligence is masking. A discrepancy model compares this student's average achievement to their average overall IQ score and finds no significant gap. A PSW model finds profound processing weaknesses causing unexpected decoding failures — the hallmark of dyslexia.

This second population is particularly important for parents of bright children who are told "they are coping fine." Their processing profile is not fine. They are spending enormous cognitive effort to maintain average output. That unsustainable expenditure is the disability.

Using PSW in an IEP Eligibility Meeting

If your child has been evaluated and the school has denied SLD eligibility based on "not low enough" achievement scores, the PSW framework is your primary rebuttal tool.

The argument:

1. Present the CTOPP-2 scores showing phonological awareness and/or RAN at or below the 16th percentile
2. Present the WISC-V profile showing the discrepancy between Verbal Comprehension and Processing Speed/Working Memory
3. Present the WIAT-4 Pseudoword Decoding score (which isolates phonetic decoding from compensatory strategies)
4. Argue that this pattern — specific processing deficits directly connected to reading difficulties, in a student with otherwise adequate cognitive ability — satisfies the IDEA definition of a disorder in basic psychological processes

If the school's evaluation did not include the CTOPP-2 or equivalent phonological processing measures, the evaluation is incomplete for the purpose of dyslexia identification. Under IDEA, you have the right to request an IEE (Independent Educational Evaluation) at public expense if you believe the school's evaluation was inadequate.

A Note on Different PSW Approaches

There are several formalised PSW approaches used by school psychologists:

• Concordance-Discordance Model (C-DM) by Hale and Fiorello
• Cross-Battery Assessment (XBA) by Flanagan, Ortiz, and Alfonso
• Dual Discrepancy/Consistency Model (DD/C) by Fuchs and colleagues

These approaches differ in their specific analytic frameworks but share the core principle that SLD identification should be based on the processing profile, not just achievement scores. Not all school psychologists are trained in PSW approaches — if the school's evaluator is unfamiliar with them, this is grounds for requesting an IEE by an evaluator who is.

The Dyslexia Support & Reading Intervention Kit includes a checklist for reviewing a psychoeducational evaluation to determine whether it includes the assessments needed for a PSW analysis, and scripts for requesting an IEE when the evaluation is incomplete. Understanding the PSW model transforms you from a parent saying "my child is struggling" to a parent saying "your evaluation missed the defining neurological features of dyslexia, and here is what needs to be assessed instead."

That is the shift that changes outcomes.