Two-digit number writing and arithmetic in Year 1 children: does number word inversion matter?

Early mathematical development relies upon the ability to translate between spoken number words and Arabic digits. Few studies have investigated whether differences in number word structure influence transcoding and its relationship with mathematics. We tested number writing and arithmetic in 177 German-speaking and 309 English-speaking Year 1 children. In English number words the order of tens and units (e.g., twenty-five) follows the written order of the Arabic digits (e.g., 25), whereas German number words are inverted (e.g., ‘fünfundzwanzig’, five-and-twenty). Transcoding at the item level was strongly influenced by number word inversion. German-speaking children made more errors transcoding two-digit numbers. However, English-speaking children made more errors writing teens, which are exceptional in English because of their inverted structure. Nevertheless, number writing was a significant predictor of arithmetic in both languages highlighting a significant relationship between transcoding ability and arithmetic for languages with and without number word inversion.