Problematic Smartphone Use and Adolescent Developmental Outcomes: A Three-Wave Longitudinal Analysis of Prospective Associations Through Academic Stress and Time-Use Pathways

Problematic smartphone use in adolescence has been linked cross-sectionally to poorer academic and emotional functioning, but the longitudinal mechanisms remain unclear. Using three waves of the Panel Study on Korean Children (W14–W16; ages 14–16), this study tested whether problematic smartphone use at age 14 predicts four developmental outcomes at age 16—school adjustment, self-regulated learning, ego resilience, and subjective happiness—through four age-15 mediators: gaming, video-watching, self-study hours, and academic stress. Hierarchical regressions with autoregressive controls, bootstrap a-paths, and 16 indirect effects tested with 20,000-draw Monte Carlo confidence intervals were estimated. Problematic smartphone use predicted three outcomes but not subjective happiness, for which the association was indirect only. Seven indirect effects were significant, and six survived Benjamini–Hochberg false discovery rate correction. The findings indicated two pathways: a time-displacement pathway (gaming and reduced self-study) specific to self-regulated learning and an academic-stress pathway linked to school adjustment, ego resilience, and happiness. Crucially, in baseline-controlled sensitivity analyses, the time-use pathways remained significant, whereas the stress pathway was fully attenuated, indicating a concurrent rather than a prospective association. Results were robust across path-model SEM, full-information maximum likelihood, and inverse-probability weighting, supporting a dual-pathway account of adolescent digital development.