This study examined the effects of bridging Western STEM and Indigenous Ecological Knowledge (IEK) in high school environmental science on students’ engagement, sustainability literacy, and perceptions. Anchored on the constructivist learning theories of Jean Piaget (1952) and Lev Vygotsky (1978), Methodologically, a qualitative desk-based research design was adopted, utilizing systematic documentary analysis and thematic synthesis of twenty purposively selected global sources (2015–2026) drawn from Scopus, Web of Science, and ERIC, spanning Africa, North America, Asia, and Australia. The synthesized findings revealed that: first, integrating IEK significantly enhances classroom engagement by leveraging cognitive resonance and eliminating academic alienation; second, bridging these models transforms sustainability literacy into localized, context-specific action competence; and third, initial epistemic friction transitions into profound cultural validation. The study concludes that resolving modern environmental and educational crises requires a systemic transition from epistemic hegemony to institutionalized knowledge pluralism where scientific innovation and ecological stewardship are viewed as universally shared human endeavours. To operationalize this integrated architecture, it is recommended that ministries structurally mandate IEK-STEM integration within secondary curricula, policy planners shift environmental education guidelines toward community-centered resource-management paradigms, and teacher certification boards introduce mandatory professional training in decolonial and inclusive pedagogies to equip educators with essential cross-cultural instructional strategies.

Keywords: Constructivism, Decolonial Pedagogy, Environmental Science, Indigenous Ecological Knowledge, Student Engagement, Sustainability Literacy, Western STEM.