The Reasoning Was Intact; the Bookkeeping Was Not

What the research found

A team led by Marika Iaia at the University of Salento set out to answer a narrow question. When adults with dyslexia sit the standard adult intelligence test, the WAIS-IV, where exactly do their scores dip, and where do they hold firm? The answer matters because dyslexia is often described as a reading problem, yet its effects reach further than the page.

The study compared 71 native Italian speakers at university. Thirty-six had a diagnosis of dyslexia; thirty-five did not. All had a full-scale IQ of at least 85, so nobody in the sample had a general intellectual difficulty. The average age was around 23. This was, in other words, a group of capable young adults who had made it into higher education, tested on four separate cognitive skills.

Two of those four skills were untouched. Verbal comprehension, which measures vocabulary and the ability to reason with words, was essentially identical across the two groups: 107 in the dyslexia group against 109 in the controls. Perceptual reasoning, which measures the handling of visual patterns and problems, was the same story: 104 against 106. On the parts of the test that most people think of as “thinking,” the students with dyslexia were indistinguishable from their peers.

The other two skills told a different story. Working memory, the ability to hold and juggle information in the mind for a few seconds, fell to 91 in the dyslexia group against 103 in the controls. Processing speed, the ability to carry out simple mental tasks quickly and accurately, fell to 94 against 109. Both gaps were large in statistical terms, with effect sizes near or above one standard deviation. The individual tasks that suffered most were mental arithmetic, and two timed clerical tasks called Coding and Symbol Search, all of which lean heavily on speed and short-term holding.

There is a subtle point buried in the headline scores. The full-scale IQ of the dyslexia group came out at 100, nine points below the controls, yet this number is misleading. Because working memory and processing speed drag the overall figure down, the full-scale score understates the reasoning ability of a dyslexic adult. When the authors used a measure that strips those two elements out, the General Ability Index, the gap between the groups nearly vanished: 106 against 108. The authors report that the four-index pattern, taken together, distinguished dyslexic from non-dyslexic adults fairly well, with a discrimination statistic of 0.82.

What it means for you and your child

The practical lesson is that a single IQ figure can quietly misrepresent a dyslexic learner. If your child has been given one number, and that number sits below what you see in their conversation, their curiosity, or their grasp of ideas, this study offers a plausible reason. The composite score is pulled down by speed and short-term memory, not by the capacity to reason. Ask whether the assessor reported the separate indices, and in particular the General Ability Index, which the authors here found far more flattering and, arguably, far more honest.

It also reframes what dyslexia support is for. If reasoning is intact and the bottleneck is holding information and working at pace, then the accommodations that help are the ones that relieve those two pressures. Extra time in examinations is not a courtesy; it directly offsets a measured processing-speed gap. So do practical habits: writing steps down rather than holding them in the head, breaking multi-part instructions into single lines, and reducing the number of things that must be juggled at once. Mental arithmetic was among the weakest tasks here, which is worth remembering before concluding that a bright child is simply bad at maths.

Be careful, though, about how far you carry these findings. This was a modest sample of 71 people, and the authors are candid about its limits. University students are, by definition, the dyslexic adults who succeeded academically, so the profile may look milder than it would in the wider population. Italian is a “transparent” language, meaning its spelling maps cleanly onto its sounds, and the authors caution that the pattern may differ in English, where the code is far messier. The study is a snapshot, not a life story, and it cannot tell you how any one child will fare.

Nor does it establish cause. The study shows that dyslexia and weaker working memory travel together in this group; it does not prove that one produces the other, and the relationship may well run in both directions or share a common root. A single study, however clean, describes a pattern rather than settling a mechanism. Treat these numbers as a well-measured description of where the difficulty tends to sit, not as a verdict on your child.

What you can take away is quietly reassuring. In this sample, dyslexia left the machinery of reasoning alone. The struggle was with speed and short-term memory, both of which can be supported, worked around, and, above all, kept from being mistaken for a limit on the mind itself.