The natural number bias and its role in rational number understanding in children with dyscalculia. Delay or deficit?
Kids with dyscalculia need help catching and correcting the natural-number bias when they meet fractions and decimals.
01Research in Context
What this study did
Van Hoof et al. (2017) compared kids with dyscalculia to same-age peers and to younger kids who matched their math level.
They gave tasks that tested fractions and decimals.
The goal was to see if the dyscalculia group had a true delay or a lasting deficit.
What they found
Kids with dyscalculia scored far below their age mates on every rational-number task.
Their scores looked like those of younger kids with the same math skill level.
The gap grew when problems triggered the natural-number bias, the gut feeling that bigger numbers are always bigger values.
How this fits with other research
Wachob et al. (2015) and Fernández-Cobos et al. (2025) also found math trouble in autistic kids, yet many teachers still expect math strength in autism.
These papers do not clash; they simply show different groups can struggle for different reasons.
Crollen et al. (2015) used the same compare-to-controls method in kids with non-verbal learning disability and likewise saw a clear, specific weakness, backing the idea that narrow math disorders exist.
Why it matters
If a child with dyscalculia keeps applying whole-number rules to fractions, extra practice alone will not fix it.
You need to build activities that make the conflict visible, like shading bar models that show ½ is larger than ¼ even though 2 is smaller than 4.
Spot the bias early and teach kids how to stop and check their first gut answer.
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02At a glance
03Original abstract
BACKGROUND: Previous research indicated that in several cases learners' errors on rational number tasks can be attributed to learners' tendency to (wrongly) apply natural number properties. There exists a large body of literature both on learners' struggle with understanding the rational number system and on the role of the natural number bias in this struggle. However, little is known about this phenomenon in learners with dyscalculia. AIMS: We investigated the rational number understanding of learners with dyscalculia and compared it with the rational number understanding of learners without dyscalculia. METHOD: Three groups of learners were included: sixth graders with dyscalculia, a chronological age match group, and an ability match group. RESULTS: The results showed that the rational number understanding of learners with dyscalculia is significantly lower than that of typically developing peers, but not significantly different from younger learners, even after statistically controlling for mathematics achievement. CONCLUSION: Next to a delay in their mathematics achievement, learners with dyscalculia seem to have an extra delay in their rational number understanding, compared with peers. This is especially the case in those rational number tasks where one has to inhibit natural number knowledge to come to the right answer.
Research in developmental disabilities, 2017 · doi:10.1016/j.ridd.2017.10.006