This case study examines the shifting bilingual preference of three French/Englishbilingual children over a three-year period. It also clarifies the distinction between the manyoften misleading terms used to refer to bilingual preference (i.e., a bilingual's languagechoice). The children's fluctuating bilingual preference is accounted for in terms of threecontextual domains: home, school, and community. The home domain was predominantlyFrench-speaking, while the community domain shifted between predominantly English-speakingLouisiana and French-speaking Québec. The 10-year-old identical twin girls were in aFrench immersion program in Louisiana during the entire three-year period; their 12-year-oldbrother was not. A new, domain-sensitive longitudinal measure – the bilingual preferenceratio (BPR) – was created and applied for each child using 36 months of weekly taperecordings of mealtime conversations. BPR fluctuations indicate that the greatest effect on thechildren's language preference was community immersion in the target language.However, the twins' markedly greater preference for speaking French at home inLouisiana is attributed to the influence of French immersion at school.