This ethnographic case study explores a bilingual child's academic socialization in both formal and informal academic communities. It observes a high-achieving, bilingual student in a public US primary school, who paradoxically is regarded as a slow learner in her Korean-American Sunday school. From the academic socialization and community of practice views, 360 contextual, interactional, and interview events collected from both communities over a one year course are examined. Explicit norms and peer collaboration notably affect a child's socialization in a formal academic school context, and the mild, unruly setting and various language ideologies extant in an informal bilingual academic context, like a church's Sunday school, also notably affect a child's socialization. This study debates how a bilingual child builds multilingual and multicultural skills and identities via distinct and even inconsistent socialization experiences from two diverse learning contexts.