Wechsler Intelligence Scale for Children (WISC)

The Wechsler Intelligence Scale for Children is an individually administered test of cognitive ability for children aged 6 to 16 years. It provides a full scale intelligence quotient and index scores for verbal comprehension, visual spatial ability, fluid reasoning, working memory and processing speed.

Scores are normed by age, with a mean of 100 and an SD of 15. A clinical psychologist administers the test, which takes about 60 to 90 minutes.

Usage. It is used to assess learning difficulties, intellectual disability, giftedness, and cognitive effects of neurological illness, and to plan educational support.

Indications. Suspected intellectual disability, specific learning difficulty, school difficulties, cognitive effects of brain injury, epilepsy or chronic illness, and assessment for educational support.

Preparation and technique. The child is assessed in a quiet room, rested and fed. The examiner builds rapport before testing, and breaks are given as needed. Observations of attention, effort and behaviour are recorded.

Contraindications and precautions. Acute illness, emotional distress, sedating medicines and sensory impairment reduce validity. Children whose first language differs from the test language need adapted assessment.

Interpretation.

• An FSIQ of 90 to 109 is in the average range.
• An FSIQ of 70 or under falls at about two SDs under the mean and is one element in the assessment of intellectual disability.
• A diagnosis of intellectual disability needs impaired adaptive functioning as well as a low score.
• Uneven profiles between indices point to specific learning difficulties, language disorder or attention problems.

Causes of a low score. Intellectual disability, language disorder, hearing or visual impairment, attention deficit disorders, emotional distress, and environmental deprivation.

Critical values and findings needing immediate action. Regression in cognitive ability, loss of previously acquired skills, or new neurological signs requires urgent medical assessment.

Limitations and artefacts. A single score is influenced by the child's mood, effort and the testing context. Practice effects limit retesting within a short interval. Cultural and language factors lower validity.

Follow up tests. Assessment of adaptive behaviour, speech and language assessment, audiology, vision assessment, genetic testing where intellectual disability is present, and neuroimaging where neurological signs exist.

Special groups. Children with cerebral palsy or sensory impairment need adapted versions. Preterm children are assessed using age appropriate expectations. Children from bilingual backgrounds may be better assessed using non-verbal indices.