Processing Speed and Working Memory Explained

The Child Who Went Upstairs and Forgot Why

A mum in Bella Vista asks her eight-year-old to do four things. “Go upstairs, put your pyjamas on, brush your teeth, and come down for a story.” Five minutes later he is standing in his pyjamas on the landing. He looks puzzled. He has no idea what comes next.

His mum is sure he is not listening. His teacher says the same thing. The boy starts to believe it too.

But he may be listening perfectly well. The problem may be somewhere else. He may simply not be able to hold four steps in his head at once. That is working memory. And it is one of two scores on a cognitive assessment report that people often skip past.

This article explains what processing speed and working memory are. It covers what the WISC-V and WAIS-IV measure, why the two scores matter for ADHD and learning, and what can help. It comes from our team of IQ assessment psychologists in Bella Vista.

Why These Two Scores Get Overlooked

If you have ever read a cognitive assessment report, you probably looked for one number first. That number is the Full Scale IQ. It is the number from films and TV. It is the number most people know how to talk about.

In clinical practice, though, the Full Scale IQ is often the least useful part of the report. The real story is in the pattern across the index scores. An index score groups several related tasks into one measure, such as verbal reasoning or memory.

Two of those indices often explain the most about daily life. They are Processing Speed and Working Memory. Most people never think about them until something goes wrong.

Which Test Is Which

Two Wechsler tests are used most often:

• WISC-V is for children, roughly ages 6 to 16.
• WAIS-IV is for people from age 16. The newer WAIS-5 is being progressively adopted.

You can read more about each in our guides to the WISC-V child cognitive assessment and WAIS adult IQ and cognitive assessment.

What Processing Speed Actually Is

Processing speed is how fast a person can take in simple visual information and respond to it. Think of it as the “clock speed” of routine thinking. It is not how deep your reasoning goes. It is not how much you know. It is not how creative you are.

On the WISC-V, processing speed is measured by three subtests:

• Coding. Match symbols to numbers against the clock.
• Symbol Search. Scan a row of symbols to see if a target is there.
• Cancellation. Cross out target pictures among distractors.

The Processing Speed Index (PSI) comes from Coding and Symbol Search.

On the WAIS-IV, the two core subtests are also Coding and Symbol Search. They are adult versions of the child tasks.

The tasks look very simple. There is no puzzle to solve. That is the point. Because the tasks are so simple, the only thing that differs between people is how fast they can do them.

Processing speed matters because it touches almost everything else. Reading fluency depends on it. So does writing, keeping up with a fast conversation, and finishing a routine within a time limit. When processing speed is low, all of these can feel harder than a person’s other strengths would predict.

Many things can lower processing speed. Clinicians look at each one:

• ADHD. Lower processing speed is a common finding in children and adults with ADHD. It is not universal. Some people with ADHD have average or higher processing speed.
• Anxiety and depression. Both can slow processing speed. A test done during an untreated depressive episode may show a lower score than the person’s usual level.
• Sleep. Long-term and short-term sleep loss both reduce processing speed.
• Concussion and brain injury. Processing speed is one of the areas most often affected.
• Chronic illness. Conditions such as long COVID, multiple sclerosis and chronic fatigue can reduce it.
• Age. Processing speed usually eases gradually from midlife. This is a normal pattern.
• Some medications. Certain sedating medicines can slow processing speed as a side effect.

When the Processing Speed score is low, the psychologist’s job is to work out which of these is behind it. The support that helps depends on the cause.

What Working Memory Actually Is

Working memory is the ability to hold information in mind while you work with it. It is the mental workspace where thinking happens.

Here are some everyday examples:

• Holding a phone number in your head while you find your phone.
• Remembering step three of a recipe while you do step two.
• Remembering how a sentence started so you can reply to how it ends.
• Holding a middle answer in mind during a maths problem.

On the WISC-V, working memory is measured by three subtests:

• Digit Span. Repeat strings of numbers forwards, backwards and in order.
• Picture Span. Remember the order of pictures shown briefly.
• Letter-Number Sequencing. Hold a mix of letters and numbers in mind and put them in order.

The Working Memory Index (WMI) comes from Digit Span and Picture Span.

On the WAIS-IV, the two core subtests are Digit Span and Arithmetic. Arithmetic is mental maths read out loud. It makes you hold numbers in mind while you work on them.

Clinicians also look at two parts of working memory. One is capacity: how much a person can hold at once. The other is manipulation: whether they can work on the information while holding it. Digit Span Forward mostly shows capacity. Digit Span Backward and sequencing show both.

Working memory matters for reading comprehension, writing, multi-step instructions, mental maths and conversation. Many of the same factors that affect processing speed can affect it too:

• ADHD. Working memory difficulties are a core feature of ADHD.
• Anxiety. Worry takes up mental space. The more room worry fills, the less is left for the task.
• Depression. It can lower working memory, which adds to concentration problems.
• Sleep. Poor sleep reduces working memory, especially the “working on it” part.
• Specific learning disorders. Lower working memory is a common contributor to dyslexia, dysgraphia and dyscalculia.
• Age and neurological conditions. Some change with age is normal. Concussion, stroke and other conditions can also affect it.

Again, when the Working Memory score is low, the psychologist works out which factor is behind it.

Why One IQ Number Can Describe Nobody

The Full Scale IQ is a summary of the index scores. When the indices are close to each other, it is a fair summary. When they are far apart, it stops being useful. It averages strengths and weaknesses that mean very different things in daily life.

Here is an illustrative profile:

• Verbal Comprehension: 90th percentile
• Fluid Reasoning: 88th percentile
• Visual Spatial: 82nd percentile
• Working Memory: 25th percentile
• Processing Speed: 12th percentile

A percentile shows how a person scored compared with others of the same age. The 90th percentile means they scored higher than about 90 out of 100 people.

This profile would produce a Full Scale IQ somewhere in the average range. But “average” does not describe this person at all. They are likely to be sharp, clear speakers and creative thinkers. At the same time they may struggle with speed-based tasks, multi-step instructions, fast conversations and deadlines.

The average hides both halves of the picture. It is not accurate for the strengths, and it is not accurate for the struggles. The individual indices show what the single number cannot.

A profile like this is a common pattern in adult ADHD assessments. It is often what parents mean by “so bright but so scattered”. Adults sometimes say “smart but slow”. Even so, the profile alone does not diagnose anything.

A smaller dip in just one of the two “efficiency” indices (Working Memory or Processing Speed) can also point to something worth looking into. That might be ADHD, anxiety, sleep or a learning difficulty.

For more on the tests themselves, see IQ testing near me: what to expect in Bella Vista.

Low Processing Speed in Real Life

Here is what low processing speed can look like.

In a child:

• They are often the last to finish work, even when they know the material.
• They may miss the second half of a fast instruction.
• They may do badly on timed tests but well on the same questions with more time.
• They may go quiet in group talk because the conversation moves on before they are ready.
• They may come home very tired, because keeping up with the pace took so much effort.

In an adult:

• They may call themselves “not a fast thinker” or “someone who needs to sleep on things”.
• They may do well in roles that reward depth and careful thought.
• They may find fast task-switching, phone work or quick brainstorming harder.
• They may find writing easier than talking, because writing gives them time.
• They may find fast-paced meetings tiring.

Neither person is less intelligent than someone with average processing speed. They have a specific limit on rate, and it shows up in specific kinds of tasks.

Low Working Memory in Real Life

In a child:

• They find multi-step instructions hard, like the pyjamas story above.
• They forget what they came into a room for.
• They lose track of what they were doing after an interruption.
• They struggle with mental maths.
• They may seem not to listen, when they actually cannot hold a long spoken instruction in mind.

In an adult:

• They may rely on lists, calendar reminders, phone notes and alarms.
• They may find long meetings tiring.
• They may prefer email to phone calls, because email leaves a record.
• They may find it hard to summarise a long article, even though they understood it.

Again, neither person is less intelligent. They have a specific limit on capacity.

Why This Pattern Matters for ADHD

ADHD is not a problem with intelligence. People with ADHD span the whole range of ability. At a thinking level, ADHD is largely a difference in executive functioning. That means the skills that manage attention, working memory, impulse control, planning and goal-directed behaviour.

Working memory is one of those core skills. Lower working memory is well documented in ADHD. It helps explain common daily struggles: losing track of tasks, forgetting instructions and holding long plans in mind.

Processing speed is not strictly an executive function. But lower processing speed often goes along with ADHD in adults. Being slower to process and less able to hold things in mind can make the world feel more overwhelming than either one alone would.

When a cognitive assessment shows this pattern, it can add supporting evidence. This is most useful when there are also other signs, such as developmental history, impact across settings and screening tools like the ASRS or DIVA-5.

But please be clear on one point. A cognitive assessment does not diagnose ADHD on its own. ADHD is diagnosed clinically, using DSM-5-TR or ICD-11 criteria applied to a person’s history and current life. The assessment is a supporting piece, not the final word.

After a diagnosis, psychological therapy can help people work with their profile rather than against it. This may include CBT for patterns like procrastination and task avoidance, and ACT for values and committed action. For parents, it may include emotion coaching. You can read more about ADHD psychology support in Bella Vista.

Why This Pattern Matters for Learning

Working memory and processing speed are two of the most common thinking factors behind specific learning disorders such as dyslexia, dysgraphia and dyscalculia.

• Working memory and reading. The reader must hold the start of a sentence in mind while reading the end. A child may read each word correctly but lose the thread of a longer text.
• Working memory and maths. Multi-step problems need middle answers held in mind. A child may get them wrong in their head but right when each step is written down.
• Working memory and writing. The writer must hold the shape of what they want to say. Written work may become fragmented or jump between ideas.
• Processing speed and reading fluency. A child may read accurately but slowly. The effort of decoding can take space away from meaning, and long reading can be tiring.
• Processing speed and written output. A child may write very well at home with unlimited time, and much less well in class under normal time limits.

For more, see our guides on dyslexia and learning difficulty assessment for children and the WIAT-III academic achievement test.

Practical Strategies for Low Processing Speed

If an assessment finds low processing speed, these are the strategies most often suggested.

• Reduce time pressure where you can. For children, this may mean school adjustments such as extra time, less writing or chunked homework. For adults, it may mean roles and workflows that reward depth over speed.
• Batch tasks by rhythm. Group fast tasks like email together. Group slow tasks like deep analysis together. Constant switching is harder.
• Build in buffer time. Tight schedules are hard on a slower processor. Spare time around transitions and deadlines reduces the feeling of never catching up.
• Use writing to think. Writing is slower than talking, which can suit a slower processor. Moving some conversations into email or notes can help.
• Give permission to be slow. Adults can say “take your time” and mean it. This helps children to see their pace as a difference, not a failing.
• Reduce interruptions. It takes longer to get back into a task after an interruption. Quiet spaces and do-not-disturb time help.
• Look after the basics. Sleep, exercise and mood all affect processing speed. This is not the whole answer, but it is often part of it.

Practical Strategies for Low Working Memory

If low working memory is part of the profile, these are the strategies most often suggested.

• Put memory outside your head. Lists, reminders, phone notes and checklists all take load off working memory.
• Chunk multi-step instructions. Break a five-step task into smaller parts with checkpoints. A whiteboard or visual schedule helps children.
• Repeat it back. Asking the person to say the instruction in their own words catches problems early.
• Reduce distractions. Noise, clutter and background talk use up the same limited space. A quiet, tidy spot helps.
• Use visual supports. Diagrams, mind maps, flowcharts and written summaries lower the load of complex information.
• Address anxiety and worry. Worry competes for working memory. Treating anxiety, for example with CBT or ACT, may ease that pressure.
• Look after the basics. Sleep and mood affect working memory too.

Common Myths, Cleared Up

These are things people often believe. Each one is a myth.

Myth: “Low processing speed means low intelligence.” This is false. Processing speed is one of five index areas on the WISC-V and one of four on the WAIS-IV. The point of having several indices is that these areas can be separated. A person can have strong reasoning and low processing speed.

Myth: “Low working memory means they are not trying hard enough,” or “just concentrate harder.” This is false. Working memory is a capacity limit. It is not a motivation problem. Telling a child to “concentrate harder” does not increase their capacity. It adds shame to a hard situation. Changes to the environment help more than telling someone to try harder.

Myth: “ADHD medication will fix low working memory or processing speed.” This is only partly true. Medication can help working memory and processing speed in some people with ADHD, and that is one way it helps with daily life. But it is one part of the picture, not the whole. It is not a cognitive enhancer for everyone. Adjustments, therapy and lifestyle matter too. Any medication decision is made with a prescribing GP or psychiatrist.

Myth: “Brain-training apps can permanently increase working memory.” Current evidence does not support this. Commercial brain-training programmes usually improve the specific tasks trained. They do not reliably carry over to real life (Melby-Lervåg et al., 2016; Cortese et al., 2015). Support such as adjustments, memory aids and treating contributing factors is usually a better use of effort.

Myth: “A cognitive assessment will tell me if I have ADHD.” This is false. The assessment is one supporting piece. ADHD is diagnosed clinically, from developmental history, current impact and standardised tools like the DIVA-5 for adults. A profile can be consistent with ADHD, but the diagnosis is a clinical judgement.

Three Composite Examples

None of these is a real person. Each is a pattern that comes up often.

The “smart but scattered” adult. A woman in her early thirties has an assessment as part of an adult ADHD workup. Her Verbal Comprehension is at the 91st percentile and Fluid Reasoning at the 87th. Her Working Memory is at the 30th and Processing Speed at the 14th. Her Full Scale IQ falls in the average range, which on its own would mislead. In daily life this can look like strong strategic thinking alongside trouble keeping up with email and multi-step tasks. Therapy may involve seeing the profile clearly, reshaping work around her real rhythms, building outside memory systems, and working through years of shame about not being able to “just do it”.

The Year 4 boy who “won’t listen”. A ten-year-old is referred because school is worried about attention and following instructions. His WISC-V shows average Verbal Comprehension and Visual Spatial, above-average Fluid Reasoning, and low-range Working Memory and Processing Speed. Teacher and parent rating scales fit with ADHD. The profile does not diagnose ADHD by itself, but it fits with what the interview and ratings suggest. Support may include chunked instructions and visual supports at school, and a medication review with a paediatric doctor. It may also include helping him understand himself. He has been told he is “not listening”. Learning that his brain cannot hold a five-step instruction the way his classmates’ can may reduce his defensiveness.

The adult recovering from concussion. A man in his late forties has an assessment nine months after a concussion. He feels his reasoning is fine, but everything is slower and takes more effort. His Verbal Comprehension and Fluid Reasoning are solidly above average. His Processing Speed is at the 25th percentile, probably below his level before the injury. His Working Memory is at the 50th percentile. The picture is consistent with ongoing change after concussion. Recommendations may include a phased return to work, less time pressure, links with his rehabilitation team, and a repeat assessment in six to twelve months to track change.

In all three, the two “efficiency” indices carried the most day-to-day meaning, even though the reasoning scores draw the eye first.

A Note on the WISC-V Working Memory Split

If you have a WISC-V report, there is a small technical point. The WISC-V has a Working Memory Index, based on Digit Span and Picture Span. One task is verbal and one is visual. It also has an Auditory Working Memory Index, based on Digit Span and Letter-Number Sequencing. Both of those tasks are verbal.

If your report shows both, check whether the scores are similar or different. Some children find verbal working memory harder than visual. A child with weaker verbal working memory but stronger visual working memory is likely to do better with visual supports.

Cost, Wait Times and Rebates

We do not want to quote figures that go out of date. These details can change, so please confirm current information with reception.

• Cost. A full cognitive assessment (WISC-V or WAIS-IV, with a report and feedback) is a large piece of clinical work. Adding an achievement test (WIAT-III) or extra measures for ADHD or dyslexia questions raises the total. In Australian private practice the total is typically in the low-to-mid four figures.
• Wait time. Wait times vary. Reception can give you an honest current figure.
• Medicare. Rebates for cognitive assessment are limited. A standard Mental Health Care Plan from a GP does not fund a full cognitive assessment. Rebates for therapy sessions are available with a plan from your GP.
• NDIS. For some NDIS participants, funding for assessment may be possible under capacity-building supports. This depends on the individual plan. Potentialz Unlimited is not a registered NDIS provider, so please check how this applies to you before booking.
• Private health insurance. Some funds cover part of a psychological assessment. Check with your insurer.

What Happens After the Report

A report on its own changes nothing. The value comes from turning it into changes in daily life.

For children, this often means:

• Sharing the report with school and asking for learning adjustments, such as extra time, chunked instructions and visual supports.
• Changing home routines around homework and morning and evening transitions.
• Thinking about whether a further assessment is needed, for ADHD or a specific learning disorder.
• Therapy for the worry, low confidence or school distress that has built up.

For adults, this often means:

• Reviewing work patterns and moving toward rhythms that fit the profile.
• Building better outside memory systems.
• Thinking about whether a formal ADHD assessment is needed, with a psychiatrist or a GP experienced in ADHD.
• Therapy or coaching around ADHD-related patterns, anxiety, or adjusting to naming a long-standing pattern for the first time.

Cognitive Assessment in Bella Vista and the Hills District

Potentialz Unlimited is based in Bella Vista, NSW, and supports individuals and families across the Hills District, including Norwest, Castle Hill, Kellyville, Baulkham Hills and Rouse Hill.

Formal cognitive assessment (WISC-V, WAIS and WIAT-III) is delivered in person by Dr Gurprit Ganda, our senior Clinical Psychologist. Our other registered psychologists offer therapy and coaching before and after an assessment. This can include helping you work out what question to bring, and turning a report into practical changes.

If you are unsure whether an assessment is the right step, a short phone call with reception is usually more useful than a form. Reception can talk through the question you want answered, and the current cost, wait time and rebate details. You can contact the clinic or book online at live.potentialz.com.au.

Disclaimer

The information in this article is general in nature. It is not clinical advice for your situation. Please speak with a qualified health professional about your own circumstances. If you are in crisis, contact your GP, call Lifeline on 13 11 14, or go to your nearest emergency department.

Crisis and Support Resources

• Lifeline: 13 11 14 (24/7)
• Beyond Blue: 1300 22 4636
• Kids Helpline: 1800 55 1800
• MensLine Australia: 1300 78 99 78
• 13YARN (Aboriginal and Torres Strait Islander crisis line): 13 92 76
• Emergency: 000

---

References

Alloway, T. P., & Alloway, R. G. (2010). Investigating the predictive roles of working memory and IQ in academic attainment. Journal of Experimental Child Psychology, 106(1), 20–29. https://doi.org/10.1016/j.jecp.2009.11.003

Baddeley, A. (2012). Working memory: Theories, models, and controversies. Annual Review of Psychology, 63, 1–29. https://doi.org/10.1146/annurev-psych-120710-100422

Barkley, R. A. (2015). Attention-deficit hyperactivity disorder: A handbook for diagnosis and treatment (4th ed.). Guilford Press.

Cortese, S., Ferrin, M., Brandeis, D., Buitelaar, J., Daley, D., Dittmann, R. W., … Sonuga-Barke, E. J. (2015). Cognitive training for attention-deficit/hyperactivity disorder: Meta-analysis of clinical and neuropsychological outcomes from randomized controlled trials. Journal of the American Academy of Child & Adolescent Psychiatry, 54(3), 164–174. https://doi.org/10.1016/j.jaac.2014.12.010

Flanagan, D. P., & Alfonso, V. C. (2017). Essentials of WISC-V assessment. John Wiley & Sons.

Kaufman, A. S., Raiford, S. E., & Coalson, D. L. (2016). Intelligent testing with the WISC-V. John Wiley & Sons.

Kofler, M. J., Rapport, M. D., Sarver, D. E., Raiker, J. S., Orban, S. A., Friedman, L. M., & Kolomeyer, E. G. (2013). Reaction time variability in ADHD: A meta-analytic review of 319 studies. Clinical Psychology Review, 33(6), 795–811. https://doi.org/10.1016/j.cpr.2013.06.001

Lichtenberger, E. O., & Kaufman, A. S. (2013). Essentials of WAIS-IV assessment (2nd ed.). John Wiley & Sons.

Melby-Lervåg, M., Redick, T. S., & Hulme, C. (2016). Working memory training does not improve performance on measures of intelligence or other measures of “far transfer”: Evidence from a meta-analytic review. Perspectives on Psychological Science, 11(4), 512–534. https://doi.org/10.1177/1745691616635612

Nigg, J. T. (2013). Attention-deficit/hyperactivity disorder and adverse health outcomes. Clinical Psychology Review, 33(2), 215–228. https://doi.org/10.1016/j.cpr.2012.11.005

Sattler, J. M. (2018). Assessment of children: Cognitive foundations and applications (6th ed.). Jerome M. Sattler, Publisher.

Wechsler, D. (2008). Wechsler Adult Intelligence Scale — Fourth Edition (WAIS-IV): Technical and interpretive manual. Pearson.

Wechsler, D. (2014). Wechsler Intelligence Scale for Children — Fifth Edition (WISC-V): Technical and interpretive manual. Pearson.

Weiss, L. G., Saklofske, D. H., Holdnack, J. A., & Prifitera, A. (Eds.). (2019). WISC-V: Clinical use and interpretation (2nd ed.). Academic Press.

---