--- - |2 Abstract Family socioeconomic status (SES) is strongly associated with children's cognitive development, and past studies have reported socioeconomic disparities in both neurocognitive skills and brain structure across childhood. In other studies, bilingualism has been associated with cognitive advantages and differences in brain structure across the lifespan. The aim of the current study is to concurrently examine the joint and independent associations between family SES and dual‐language use with brain structure and cognitive skills during childhood. A subset of data from the Pediatric Imaging, Neurocognition and Genetics (PING) study was analyzed; propensity score matching established an equal sample (N = 562) of monolinguals and dual‐language users with similar socio‐demographic characteristics (Mage = 13.5, Range = 3–20 years). When collapsing across all ages, SES was linked to both brain structure and cognitive skills. When examining differences by age group, brain structure was significantly associated with both income and dual‐language use during adolescence, but not earlier in childhood. Additionally, in adolescence, a significant interaction between dual‐language use and SES was found, with no difference in cortical surface area (SA) between language groups of higher‐SES backgrounds but significantly increased SA for dual‐language users from lower‐SES families compared to SES‐matched monolinguals. These results suggest both independent and interacting associations between SES and dual‐language use with brain development. To our knowledge, this is the first study to concurrently examine dual‐language use and socioeconomic differences in brain structure during childhood and adolescence. - Developmental Science, Volume 21, Issue 6, November 2018.