Dyslexia affects a person’s ability to read and spell, stemming from difficulty with language processing. It is not a problem with vision or a reflection of overall intelligence, but rather a difference in how the brain processes the sounds of language and connects them to letters. A diagnosis is never based on a single test score. Instead, it requires a comprehensive evaluation that systematically examines a person’s history, academic performance, and underlying cognitive skills to establish a clear profile of strengths and weaknesses.
The Intake Process and Preliminary Screening
The evaluation starts with a thorough gathering of historical information. This preliminary step involves collecting developmental, medical, and educational records. The professional reviews early language milestones, family history of reading difficulties, and previous educational interventions.
Initial screening must rule out other possible causes for reading difficulties. Problems with vision or hearing can impede reading, even if they are not dyslexia. Preliminary checks for visual and auditory acuity ensure that poor sensory input is not the primary factor explaining academic struggles.
The referral source provides data regarding observed difficulties, such as a student avoiding reading aloud or struggling with rhyming games. This anecdotal evidence helps focus the subsequent formal assessment. Documenting the history and eliminating external factors prepares the evaluator for specialized testing.
Measuring Academic Achievement
After the preliminary intake, the evaluation measures the person’s academic achievement. This phase uses standardized, norm-referenced achievement batteries to quantify deficits in core academic skills compared to peers. These tests establish how far a person’s skills deviate from the expected standard.
Common tools include the Woodcock-Johnson Test of Achievement (WJ-IV) and the Wechsler Individual Achievement Test (WIAT-III or WIAT-4). These batteries assess the skills most affected by dyslexia, including:
- Word recognition, which assesses the ability to accurately read single, printed words out of context.
- Reading fluency, which measures the speed and accuracy with which a person can read connected text.
- Reading comprehension, which evaluates understanding of the meaning of what has been read.
- Written expression and spelling, which quantify difficulties with encoding language into written form.
Pinpointing Specific Processing Weaknesses
The evaluation tests the underlying linguistic and cognitive weaknesses that cause reading difficulties. These tests measure how the brain processes language information, which is the core deficit in dyslexia, rather than what a person has learned. This assessment is crucial for distinguishing the disorder from other learning issues.
A primary focus is the assessment of phonological awareness—the ability to recognize and manipulate the individual sound units (phonemes) within spoken words. Tasks include identifying rhyming words, segmenting sounds (like “cat”), or blending sounds to form a word. Deficits in this area are a hallmark of dyslexia because the difficulty lies in connecting speech sounds and their written symbols.
Another domain tested is Rapid Automatic Naming (RAN). This measures the speed and ease with which a person can name a series of familiar visual stimuli, such as colors, objects, letters, or numbers. Slow naming speed is predictive of reading difficulties because it reflects a lack of automaticity in retrieving phonological information.
Phonological working memory is also assessed to see how well a person can temporarily hold and manipulate verbal information. A common task involves repeating sequences of non-words or digits spoken aloud. Weakness in this memory system can interfere with learning new vocabulary and the complex decoding process.
Finalizing the Diagnosis and Interpretation
The final stage involves synthesizing the data to determine if the findings meet the diagnostic criteria for dyslexia. This synthesis often includes results from a general cognitive assessment, or IQ test, such as the Wechsler Intelligence Scale for Children (WISC-V). The purpose of this assessment is to establish the individual’s cognitive potential across domains like verbal comprehension and fluid reasoning, not to measure academic skills.
Comparing the person’s overall cognitive ability to their significantly lower academic achievement in reading establishes that the reading difficulty is “unexpected.” This unexpected nature—where intelligence is average or above, yet reading is impaired—is a defining characteristic of dyslexia. The cognitive assessment also provides a profile of strengths and weaknesses, including scores for working memory and processing speed.
The professional team uses this comprehensive profile to conduct a differential diagnosis. This involves ruling out other conditions, such as Attention-Deficit/Hyperactivity Disorder (ADHD) or intellectual disability, that can present with similar reading challenges. The process culminates in a detailed written report that outlines the diagnosis and provides tailored recommendations for instruction and accommodation.