Subtle Increments in Socioeconomic Status and Bilingualism Jointly Affect Children’s Verbal and Nonverbal Performance

In contrast to research that examines the effects of socioeconomic status (SES) and bilingualism on development by comparing clearly disparate groups, the present study investigated the role of subtle differences in these experiences for their joint impact on performance on a verbal fluency task and an executive function (EF) task. The study involved 234 6-year-old children who were assessed for nonverbal intelligence and English vocabulary; parents completed a questionnaire providing demographic information and details about children's language experiences. Children were assigned continuous scores for SES based on parents' education and for bilingualism based on experience with non-English languages. Both continuous scores were normally distributed, so median split calculations created binary groups indicating relative levels of SES (high vs. middle) and bilingualism (more monolingual vs. more bilingual). For verbal fluency, there were no group differences in semantic fluency but phonological fluency was performed better by children from higher SES backgrounds, both in between-group and continuous analyses. For EF, the between-group analysis revealed an interaction in which bilingual children in the higher SES group outperformed all other children; nonetheless, a positive relation between degree of bilingualism and EF was significant across the whole sample. Thus, both SES and bilingualism affected language and cognitive development with limiting conditions for each experience. The discussion considers the effect of these subtle differences in SES and bilingual experience on development of essential cognitive abilities, the relation between these results and previous research, and the importance of how groups are defined in research addressing individual differences.