Adolescent Cognitive and Identity Development for Vietnamese 14–19 Learners: An Evidence-Based Foundation

This paper is the developmental-psychology keystone for a Vietnamese adolescent guidance textbook series targeting learners aged 14 to 19. It synthesises canonical and contemporary developmental-psychology literature to answer three questions: what does the evidence say about cognitive maturation, identity formation, and self-regulatory capacity across this age band; which findings replicate cross-culturally and which remain bound to Western, Educated, Industrialised, Rich, Democratic (WEIRD) samples; and what is the operational implication set for designing guidance content addressed to Vietnamese teens at age 14, 16, and 18. The synthesis is purely literature-based — no cohort empirics, no human-subjects data, in compliance with the program's 2026-04-15 no-cohort directive. The paper is honest about the WEIRD bias in the source corpus: roughly two-thirds of high-impact developmental findings derive from US/EU/Anglophone samples, and several load-bearing constructs (Marcia identity statuses, Eriksonian psychosocial stages, growth mindset, grit, ego depletion, expectancy-value motivation, dualsystems brain models) require disaggregation between robust cross-cultural finding and WEIRD-suspect extrapolation. The paper's substantive contribution is a developmental-trajectory matrix indexed by age (14, 16, 18) and domain (cognition, identity, self-regulation, motivation, peer/family relations, brain maturation), with each cell tagged as robust, WEIRD-suspect, or Vietnamese-specific. The matrix is the design specification against which subsequent volumes in the series may be calibrated. Key headline findings: cognitive control matures progressively but remains incomplete at 18; identity exploration in collectivist societies is more relational and family-mediated than in WEIRD samples; growth-mindset effects are smaller and more boundaryconditioned than the popularisation literature claims; grit's incremental validity over conscientiousness is contested; ego depletion as canonically formulated has failed pre-registered replication; the dual-systems brain model is robust in broad outline but the imbalance metaphor is being revised toward a developmentally adaptive account. Vietnamese-specific gaps in the literature are documented explicitly. The paper does not prescribe interventions; intervention design is delegated to downstream nodes.