Titone and Tiv's Systems Theory of Bilingualism aims to “urge cognitive scientists and neuroscientists to better embrace sociolinguistic and sociocultural experiences as part of their theoretical and empirical purview”. No stronger case for such a framework can be found than in studies of developmental aspects of bilingualism. In fact, inclusion of sociocultural variation has been a common feature of many studies of dual language learning for some time, especially in studies of pre-school and early-school-age learners (see Genesee, 2019, for a review). Young dual language learners – neonates, infants and toddlers, exposed to more than one language – begin life as virtual tabula rasa and are capable of learning any language with facility. As a result, their language acquisition is necessarily tied to the sociocultural parameters of the learning environments they are exposed to. Moreover, as Titone and Tiv emphasize, the immediate and ultimate purpose of language learning is communication. Thus, young dual language learners must be attuned to and acquire the sociocultural constraints and norms for communicating effectively in more than one language. While sociocultural variation is important for understanding language acquisition even among monolingual children living in relatively homogeneous monocultural environments, sociocultural variation is inherent and, indeed, enhanced in the learning environments of children acquiring more than one language insofar as each language is intimately linked with different socio-cultural parameters. Sociocultural variation can be important for understanding bilingualism in yet another way. In studies of the neuro-cognitive consequences of bilingualism, it has been reported that there is a more pronounced association between dual language exposure and activation of certain brain areas among adolescent bilinguals from relatively low SES backgrounds than bilinguals from relatively high SES backgrounds (Brito & Noble, 2018). Inclusion of sociocultural variation in research on the effects of bilingualism can reveal a more nuanced view than emerges if such variation is not considered.