The Tests Cannot Tell Them Apart

What the research found

Executive function is the set of mental skills we use to hold information in mind, resist distraction, and switch between tasks. Weakness in these skills is one of the most common reasons a bright child struggles at school. Both attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are associated with such weakness. A 2024 review in Nature Reviews Psychology by Michael Kofler and colleagues asks a harder question: can we actually tell the two apart by testing executive function? Their answer is a careful no.

This is a review, not a new experiment. The authors gather findings from many meta-analyses and studies covering children, adolescents and adults, and read them against one another. That matters for how much weight to give the conclusions. A review can show where the evidence points and where it contradicts itself. It cannot, on its own, prove that one thing causes another. Keep that in mind as the numbers accumulate.

The headline is how much the two conditions overlap. On tests of working memory, the deficits are medium-to-large and roughly comparable: effect sizes of about d = 0.54 to 0.74 for ADHD and d = 0.62 to 0.73 for ASD. An effect size, or d, simply measures how far apart two groups sit on average; around 0.5 is moderate and 0.7 is large. For inhibitory control, the ability to stop an automatic response, the figures are again close: about d = 0.52 for ADHD and d = 0.46 to 0.48 for ASD. For set shifting, moving flexibly between rules, the numbers are smaller and the gap narrow (about d = 0.35 for ADHD and d = 0.48 for ASD). In short, both groups perform moderately worse than neurotypical children across a broad range of tasks, and the profiles look more alike than different.

The second finding is about the tests themselves. Many standard clinical tools were built decades ago to detect obvious frontal-lobe injury, not the subtle patterns seen in developmental conditions. The authors report that on the widely used Wechsler scales, between 24 and 50 per cent of the variance on working memory subtests actually reflects general intelligence rather than working memory in particular. Put plainly, a chunk of what these tests measure is not the thing they claim to measure.

The measurement problem cuts deeper for diagnosis. The authors state that none of the items on the gold-standard Autism Diagnostic Interview-Revised adequately distinguish ASD from ADHD. Questionnaires filled in by parents or teachers correlate only weakly, at about r = 0.20 or lower, with how a child actually performs on a task; the two are almost telling you different things. And the choice of test changes the picture entirely. Using traditional batteries, only 33 to 50 per cent of children with ADHD show an executive function deficit. Using newer, cognitively informed measures, that figure rises to 89 per cent. The condition did not change. The instrument did.

What this means for you and your child

The practical lesson is one of humility about labels. If your child has a diagnosis of ADHD or autism, this review suggests that the executive function struggles behind it may look much the same either way, and that the assessment which produced the label may be less precise than it appears. A single score, or a single questionnaire, is a rough snapshot, not a verdict. The authors are explicit that current tools often fail to separate the two conditions cleanly.

That should change what you ask for, not make you dismiss assessment altogether. When a report lands on your desk, ask which tests were used and what they actually measure. Ask whether the working memory score is separated from general ability, or tangled up with it. Ask whether conclusions rest on a rating scale that someone ticked, or on tasks your child sat and did. These are fair questions, and the research gives you grounds to ask them.

It is also worth holding the diagnostic boundary loosely in daily life. A child does not read the manual before struggling. The behaviours you see at the kitchen table, forgetting the second half of an instruction, freezing when a plan changes, losing the thread mid-task, are describable and addressable on their own terms, whatever the label above them. The overlap this review documents is a reason to focus on the specific skill that is slipping rather than the category it sits under.

We should be honest about the limits here. This is a review, so it inherits every weakness of the studies it summarises. The authors flag that the underlying research is drawn largely from White, non-Hispanic, school-aged boys in Western countries, that studies of one condition often ignored the other despite the two frequently co-occurring, and that samples tend to exclude children with intellectual disability and over-represent so-called high-functioning autism. None of these numbers describe your individual child, and none establish cause. They describe averages across groups that may not resemble the child in front of you.

For us as tutors, the message is one we already work by. We do not treat a diagnosis as a fixed ceiling or a fixed explanation. We look at what a child can and cannot yet do, we build the specific skills that are weak, and we watch what actually changes. This review, by showing how much the labels blur and how much the tools wobble, is a quiet argument for exactly that approach: attend closely to the child, and hold the categories lightly.