• Interdependence of L1 proficiency and L2 development drives cognitive and academic outcomes; robust L1 foundations support L2 learning and broader cognitive growth, as shown in bilingual education and immersion studies [2], [13], [12], [10], [15].

• Natural sequences/universal acquisition patterns observed across child and adult learners, suggesting common learning strategies rather than language-specific routes [3], [5], [16], [7].

• Educational models (immersion, bilingual schooling) yield differential cognitive and academic outcomes, indicating structured bilingual education shapes development; evidence from St. Lambert project, immersion research, and longitudinal bilingual studies [4], [20], [19], [2].

• Metalinguistic awareness and cognitive strategy development emerge as a consequence of bilingual experience, with bilinguals outperforming monolinguals in analysis and cognitive tasks; supported by metalinguistic awareness work and cognitive strategy findings [11], [10], [13].

• Cross-language interaction and language mixing appear limited in everyday bilingual speech, challenging notions of pervasive interference but highlighting nuanced bilingual development; case studies and language mixing data point to selective influences [18], [8].