This article focuses on the development of sociolinguistic competence in a second language, (here, French being acquired by young Anglo-Montrealers) in a naturalistic context where the target language is part of daily life. Sociolinguistic competence is assessed through analysis of Anglo-Montrealers’ use of a morphosyntactic variable, Future Temporal Reference (FTR), in both French and English. Variationist analyses reveal that Anglo-Montrealers possess distinct FTR variation systems for each of the languages of their linguistic repertoire. Results show that substantial contact with native speakers is a necessary condition for detailed and complete mastery of target sociolinguistic variation, in particular because the rules that govern it are rarely, if ever, explicitly taught.