Pre-University Skill and Knowledge Investments for Vietnamese Adolescents 14–19: An Investment-Economics Synthesis with an Evidence-by-Leverage Operational Portfolio

A Vietnamese adolescent in the 14–19 age band is making a sequence of capability investments — three to five years long — whose returns are realised not in lớp 12 examinations but across the subsequent four decades of working and learning life. The high-school years are commonly framed in Vietnamese parental and school discourse as exam-preparation time, with the consequence that investments whose payoff is exam-bound (memorisation of curriculum content, narrow drilling on the THPT exam item bank, decorative volunteering and certification for university-application files) crowd out investments whose payoff is post-exam and compounding. This paper synthesises the investment-economics-of-skill literature, the deliberatepractice and expert-performance literature, the second-languageacquisition literature, the mathematical-problem-solving literature, the reading-and-Matthew-effects literature, and the labourmarket signalling literature to produce an operationally usable evidence-by-leverage portfolio for the Vietnamese 14–19 decision. The paper's contribution is a three-axis investment classification — empirical-evidence strength, leverage across university and early-career, Vietnamese feasibility — applied to eight investment classes and a set of common displacement targets. The substantive operational contribution is the investment × evidence × leverage table, which orders investments by expected discounted return rather than by popularity. The recommended operational portfolio for the Vietnamese 14–19 decision is six investments ranked by evidence × leverage × feasibility: English fluency to C1, mathematical maturity for STEM-target learners (or analogous deep-domain investment for non-STEM), sustained reading practice, deliberate-practice investment in one well-specified domain, deep-work and focus capacity, and a substantive project portfolio. Investments analysed and not recommended as primary include generic tin học cơ bản certification, decorative volunteering, learning-styles-aligned study, brain-training apps, and the broad bucket of generic "soft skills" workshops. Target is the audit-loop rigor bar, not venue submission.