Psychologists have found that bilingual children perform better than monolingual children on tests measuring executive function, including attention control, task switching, and working memory. These cognitive advantages appear regardless of which languages are spoken or the child's socioeconomic background. Researchers tested over 500 children aged 7-12, controlling for factors such as parental education and family income. The bilingual children consistently outperformed their monolingual peers across all executive function measures. Schools should therefore introduce second language instruction from an early age, as this will enhance children's cognitive development and provide them with the executive function advantages demonstrated in bilingual children. Which one of the following is an underlying assumption of the above argument?