Four-and-twenty blackbirds: The effect of number word structure at different ages

Decade-unit inversion of number words, or pronouncing 24 as ‘four-and-twenty’, is a characteristic of many languages. In the present study the effects of this characteristic on number transcription are investigated in Dutch. Analyses were performed both on the problem level and on the child level, in a large sample ranging in age from kindergarten to the end of primary school.
On the item level it was found that the presence of an inversion made numbers more difficult, although this effect was weaker in numbers with irregular unit pronunciation. On the child level, it was found that the degree of inversion error making decreased with age, but despite earlier claims, inversion errors were made in all years: even at the end of primary school we found an inversion error rate around 10%. The degree of inversion error making served as a partial mediator explaining the relationship between visuospatial working memory and mathematics. This effect was most pronounced around grade 2.