Tracy Packiam Alloway, PhD

The WISC is a standardized assessment of cognitive abilities in children aged 6 to 16 years and revised versions include the Working Memory Index.

DIGIT SPAN

The Digit Span test is a highly validated method of measuring aspects of working memory capacity, and is fast and reliable to administer. However, the method of combining forward digit span with backward digit span scores conflates verbal short-term memory and verbal working memory. This can artificially raise a student’s working memory score as they may do well on the forward digit span subtest, yet struggle in the backward digit span subtest.

LETTER-NUMBER SEQUENCING

This subtest draws heavily on the student’s knowledge of basic number skills and the alphabet. Students may perform poorly on this subtest, not because they have working memory problems, but because they struggle in remembering the alphabet or numbers in the correct sequence.

ARITHMETIC

The supplementary test, arithmetic, can also be calculated into the Working Memory Index. However, it is not clear that this test genuinely provides a direct measure of working memory measure, although it certainly would be expected that children with poor working memory would be slow to develop the necessary mathematical knowledge to support good levels of performance on this test. It is therefore not recommended that arithmetic test scores are interpreted as direct assessments of working memory.

There are other limitations to the Working Memory Index. One practical drawback is that the WISC-IV is cannot be used with children below 6 years. Another is the heavy reliance on verbal information. This raises the possibility that a student who has particular problems in handling verbal information mentally may perform at low levels on these tests simply because of the format of the material, and not because of working memory problems. For example, students who fail to develop language struggle greatly on these kinds of memory test that involve spoken language, but perform at entirely normal levels when the information that is being remembered is non-verbal - such as remembering a pattern in a grid or the location of an object on a screen. So although these children have substantial working memory problems, they are probably secondary rather than primary in nature, and they also have working memory strengths that would be undetected by administration of the WISC-IV.

Read more in Working memory and learning: A practical guide

The typical characteristics of students with poor working memory are as follows. They have normal social relationships with their peers, but are reserved in group situations in the classroom, in which they tend not to participate actively.  Their academic progress is very slow, particularly in reading and maths. They struggle to meet the working memory demands of many classroom activities, and have particularly problems in remembering and following instructions, in coping with tasks that involve combining the storage of information with demanding mental processing, and in keeping track of their progress in complex tasks.

Teachers view the students as having poor attention span and being highly distractible, features that we suggest are consequences of the loss of information that is relevant to the ongoing task from working memory, resulting in task failure and loss of focus.

While these characteristics typify the majority of students with working memory problems, they are not on their own sufficient for a definitive ‘diagnosis’. Reduced working memory capacity is not the only cause of many of these classroom difficulties, although there is growing evidence that it is the most common one.

Some students can have a broader constellation of cognitive problems of which reduced working memory capacity is only one. Several relatively common developmental disorders in which working memory is impaired, including language impairment, dyslexia, ADHD, and developmental coordination disorder (dyspraxia). Importantly, these disorders have distinct working memory strengths and weaknesses that impact academic attainment.

Clear identification of working memory problems and their underlying causes is therefore a priority, and a range of methods has now been developed to support the assessment of working memory in children. I will discuss different assessments in next week’s blog.

Excerpt taken from Working memory and learning: A practical guide.