The natural number bias and its role in rational number understanding in children with dyscalculia. Delay or deficit?

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.