Solving arithmetic problems is a cognitive task that heavily relies on
language processing. One might thus wonder whether this language-reliance
leads to qualitative differences (e.g., greater difficulties, error types,
etc.) in arithmetic for bilingual individuals who frequently have to solve
arithmetic problems in more than one language. The present study investigated
how proficiency in two languages interacts with arithmetic problem solving
throughout language acquisition in adolescents and young adults. Additionally,
we examined whether the number word structure that is specific to a given
language plays a role in number processing over and above bilingual
proficiency. We addressed these issues in a German–French educational
bilingual setting, where there is a progressive transition from German to
French as teaching language. Importantly, German and French number naming
structures differ clearly, as two-digit number names follow a unit-ten order
in German, but a ten-unit order in French. We implemented a transversal
developmental design in which bilingual pupils from grades 7, 8, 10, 11, and
young adults were asked to solve simple and complex additions in both
languages. The results confirmed that language proficiency is crucial
especially for complex addition computation. Simple additions in contrast can
be retrieved equally well in both languages after extended language practice.
Additional analyses revealed that over and above language proficiency,
language-specific number word structures (e.g., unit-ten vs. ten-unit) also
induced significant modulations of bilinguals' arithmetic performances. Taken
together, these findings support the view of a strong relation between
language and arithmetic in bilinguals