The purpose of the present study was to examine the effects of age of acquisition on verbal working memory (WM) in bilinguals. In light of previous studies that have found a bilingual advantage on non-verbal WM and less consistently on verbal WM, we included participants with native-like second language (L2) proficiency who had benefited from several years of dual language use and who did not differ from the monolinguals in terms of socioeconomic status in order to control for proficiency. Very few studies have looked at bilinguals’ performance on measures of both verbal and non-verbal memory, making it difficult to know how bilingualism influences both types of abilities in the same participants. Therefore, we also compared the groups on non-verbal WM.

Simultaneous bilingual, early successive bilinguals, and late successive bilinguals were compared with monolingual English speakers. All bilingual participants were selected using three different criteria: self-assessment ratings of English abilities, ratings of nativelikeness by a native English speaker, and scores on a L2 Cloze test. The groups did not differ significantly with respect to their L2 proficiency, or on measures of general cognitive ability.

Fifteen simultaneous bilinguals were compared with 15 early successive bilinguals and 15 late successive bilinguals who acquired English between 4–6 years of age and 7–15 years of age, respectively. The bilinguals were compared with 15 English-speaking monolinguals. Participants were compared using verbal and non-verbal short-term memory and WM tests.

All bilingual groups performed significantly better than the monolinguals on tests of verbal and non-verbal WM, thus supporting a bilingual advantage. The early and late successive bilinguals scored significantly lower than the simultaneous bilinguals, suggesting an age-of-acquisition effect among the bilinguals.

This is the first study to find a bilingual advantage on verbal WM in adults, but also the first study to report an age-of-acquisition effect in groups of bilingual adults carefully selected for their nativelikeness in the L2.