• Interdependence between first-language (L1) development and second-language and academic achievement, arguing that robust L1 skills scaffold L2 literacy, cognitive transfer, and schooling success across contexts [1] [17] [20].

• Designs and outcomes of bilingual education programs, contrasting immersion, native-language support, and broad efficacy evidence; patterns emerge about how language allocation shapes literacy and cognitive benefits in school settings [2] [4] [6] [12].

• Cognitive and metalinguistic consequences: bilingualism linked to enhanced metalinguistic awareness, strategic thinking, and cognitive growth, with variability by age and exposure [11] [8] [9] [10] [13].

• Neurolinguistic underpinnings: cerebral organization, neural substrates for two languages, and differential brain-site involvement; evidence from brain mapping and processing studies [18] [3] [19].

• Language development trajectories and classroom practices: from single lexical systems to dual-language organization, with language-choice policies, literacy development, and classroom outcomes [14] [7] [16] [10] [20].