Associations of Smartphone Use Time and Sleep Duration With Academic Performance Among Korean Adolescents by School Level

BACKGROUND: Excessive smartphone use and short sleep are common among Korean adolescents facing intense academic pressure, but few studies compare their associations with performance by school level. METHODS: We analyzed data from 48,844 students from the 20th Korea Youth Risk Behavior Survey (2024); multivariable regression analyses used 31,902 complete cases. Ordinal logistic regression was stratified by school level, and multinomial logistic regression with school-level interactions was conducted as a co-primary analysis. A three-category smartphone use-time variable (≤ 240, 241-480, and > 480 min/day) was examined in a sensitivity analysis. RESULTS: High smartphone use time (> 240 min/day) was associated with lower performance in middle school (OR = 0.47) and high school (OR = 0.65) students. Among high schoolers, shorter sleep was associated with higher odds of better performance; this pattern was absent among middle schoolers. The school level × sleep interaction was significant (p < 0.001), but the school level × use-time interaction was not. IMPLICATIONS FOR SCHOOL HEALTH POLICY, PRACTICE, AND EQUITY: The associations of smartphone use and sleep with academic performance should be interpreted and addressed in light of both school level and the broader educational and sociocultural context, including school culture and examination-related academic pressures. CONCLUSIONS: Higher smartphone use time was associated with lower academic performance across both school levels, whereas the association between sleep duration and academic performance differed by school level.