Millions of children grow up learning multiple languages, yet their outcomes vary dramatically: Some have high proficiency across languages while others have more limited abilities in some languages. This review presents a systems framework for understanding diverse trajectories in bilingual language acquisition. Drawing on systems theories, we examine how multiple levels of influence interact, from individual factors, such as maturational processes that lay the foundation, to immediate language experiences with family and educational contexts that provide learning opportunities. These experiences unfold both dynamically over time and within broader societal contexts that determine language status and community support. The framework reveals how successful bilingual development depends on alignment across system levels: Children, equipped with powerful learning abilities, must meet rich and sustained language experiences, as well as supportive social conditions. This approach illuminates systematic patterns in bilingual development and emphasizes coordinated, multilevel approaches for supporting bilingual development.
Byers‐Heinlein et al. (Wed,) studied this question.