The Psychological Assessment

“The purpose of educational psychology assessment is to piece together the puzzle of dyslexia within a particular educational and social context. This involves understanding of the literacy learning process, and the reciprocal effects of educational achievements, cognitive processes, and the instructional circumstances and the learner’s perceptions, strategies and experiences. To be useful the assessment needs to lead to workable plans of action that promote learning.”


-Dyslexia, Learning and Psychological Assessment,

BPS Report (1999) p63



1.      The educational psychologist will first consider other possible contributing causes of academic learning difficulties by taking a history. An early developmental history is usually taken, including relevant information about health, behaviour, home situation and school performance.  If other factors are present, he/she will try to assess them as contributing to or affecting overall learning.

 2.      The educational psychologist will determine the pupil’s general level of cognitive ability by administering a test such as the Wechsler Intelligence Scale for Children (WISC III) (or British Ability Scales (BAS II)). The purpose of administering an intelligence scale is to try to establish the intellectual potential of the pupil and to try to establish how his/her attainment in literacy matches (or fails to match) the measured ability. However, the relationship between measured intelligence and reading/literacy development is not straightforward and, even in the non-dyslexic population, having high intelligence does not guarantee that the individual will score highly on literacy measures.

3.      The educational psychologist will determine the pupil’s present level of achievement by administering standardised attainment tests of reading, mathematics and other related skills. He/she should measure attainment in different aspects of reading (e.g. word recognition, prose reading and reading comprehension), as well as spelling, writing and numeracy.

4.      The educational psychologist will examine the pupil’s educational history and the test results for any of the specific difficulties and discrepancies normally associated with dyslexia. She/he will check to see if the pupil’s learning difficulties are unexpected in relation to the individual’s other abilities (e.g. listening comprehension skills, numeracy skills) and educational experiences.

5.      Other tests may be administered including tests of phonological skills and abilities. There is widespread agreement that difficulty with phonological skills or with phonological processing is a powerful potential indicator of dyslexia.

6.      There is some controversy about diagnosis based solely on patterns and grouping of scores on sub-tests of intelligence scales such as WISC III.  Given that the reliability of the subtests is too low to allow diagnostic inferences to be drawn, none the less, the educational psychologist may still prudently analyse grouping of subtest scores to generate hypotheses that may or may not contribute to a diagnosis of dyslexia. 

7.      In summary, the diagnosis of dyslexia is appropriate when the educational psychologist is satisfied that the pupil’s learning difficulty cannot be explained in terms of “exclusionary factors”, which are ascertained by taking a careful history. These “exclusionary factors” include environmental factors such as poor attendance at school, historical factors such as inadequate teaching or learning opportunities, organic factors such as neurological dysfunction or other factors such as attentional or concentration difficulties.

 8.      The “inclusionary” factors which are investigated by diagnostic testing and direct observation would include difficulties (in addition to those already established in literacy skills such as reading and spelling) in such areas as:

          - phonological processing
          - short-term/working memory
          - sequencing
          - number skills
          - motor functioning


When limiting factors exist such as lack of motivation, sensory impairment or inadequate instructional or environmental opportunities, the formal diagnosis of dyslexia can be difficult. In attempting to understand why an individual experiences learning difficulties, the whole individual has to be taken into consideration, and an attempt made to separate the primary and secondary difficulties. The existence of other learning problems does not preclude the possibility of dyslexia, and dyslexia may or may not be a primary difficulty. Co-morbidity arises when dyslexia is diagnosed in the presence of another difficulty such as attention deficit.



A recent report of the British Psychological Society (1999) argued that dyslexia cannot be definitively identified on the basis of an obtained difference between intellectual ability on an IQ test and reading (and writing) skills. However, the report noted that the outcomes of IQ tests can contribute to programme planning. A profile of IQ subtest scores may point to strengths and weaknesses in particular cognitive processes underpinning reading and writing. Again the point needs to be emphasised that the reliability of subtests is not sufficiently strong to allow this profile to be regarded as more than a working hypothesis.  This hypothesis may be confirmed or rejected by more reliable subsequent evidence such as the “inclusionary factors” mentioned previously.

It should be noted, however, that the BPA perspective on the problems associated with identifying dyslexia on the basis of a discrepancy between intellectual ability and reading attainment is not unreservedly held, and such a discrepancy continues to be a criterion for access to special educational provision in many educational systems.

At present, four of the five, Education and Library Boards in Northern Ireland and the Department of Education and Science of Ireland use the discrepancy model to identify those who are eligible to access external support.

Other discrepancies have been put forward as being more useful in the diagnosis of dyslexia. For example, a significantly higher score in listening comprehension in comparison to reading comprehension has been suggested as a meaningful discrepancy to help identify dyslexia. Pupils with dyslexia also tend to perform better in oral work than written work. Many display extreme curriculum discrepancies, e.g. high achievement in a science or a technical subject or art compared to low achievement in English or other language subjects.

See Chapter 2 of the Report of the Task Group on Dyslexia and Chapter 3 of the Report of the Task Force on Dyslexia for fuller discussions on the discrepancy model and sources of additional information on this issue.