Higher smartphone use time was associated with lower academic performance across both middle and high school students, whereas the association between sleep duration and academic performance differed by school level.
Key Findings
Results
Smartphone use of more than 240 min/day was associated with lower academic performance in both middle school and high school students.
Middle school: OR = 0.47 for better performance with high smartphone use (>240 min/day).
High school: OR = 0.65 for better performance with high smartphone use.
Data came from 48,844 students in the 20th Korea Youth Risk Behavior Survey (2024); multivariable regression used 31,902 complete cases.
Ordinal logistic regression was stratified by school level.
Results
Among high school students, shorter sleep was associated with higher odds of better academic performance, but this pattern was not seen among middle school students.
The association between sleep duration and performance differed by school level.
The pattern was described as absent among middle schoolers.
Analyses used ordinal logistic regression stratified by school level.
Results
The school level × sleep interaction was significant, but the school level × smartphone use-time interaction was not.
School level × sleep interaction: p < 0.001.
School level × use-time interaction was not significant, consistent with a similar association of high smartphone use with lower performance across school levels.
Multinomial logistic regression with school-level interactions was conducted as a co-primary analysis.
Methods
A sensitivity analysis used a three-category smartphone use-time variable.
Categories were ≤240, 241-480, and >480 min/day.
This was done to examine the smartphone use-time association with finer categories than the main binary split at 240 min/day.
Conclusions
The authors conclude that associations of smartphone use and sleep with academic performance should be interpreted in light of school level and the broader educational and sociocultural context.
Contextual factors named include school culture and examination-related academic pressures.
The study frames Korean adolescents as facing intense academic pressure, with excessive smartphone use and short sleep being common.
What This Means
This study used a large national survey of Korean middle and high school students (48,844 participants, with about 31,900 having complete data for the main analyses) to look at how smartphone use time and sleep relate to self-reported academic performance. Students who used smartphones more than four hours a day were less likely to report better academic performance, in both middle school and high school. The link looked somewhat stronger in middle school (OR 0.47) than in high school (OR 0.65), but the statistical test found no clear difference between the two school levels.
Sleep told a different story. Among high school students, sleeping less was associated with a higher chance of better academic performance, while this was not seen in middle school. The difference between school levels for sleep was statistically significant. The authors suggest this may reflect Korea's intense, exam-driven school culture, in which high school students who trade sleep for study time may achieve higher grades.
This research suggests that smartphone use and sleep relate to school performance in different ways depending on age and educational setting. Because the survey captures a single point in time, it cannot show that smartphone use or sleep causes changes in grades. The finding that shorter sleep goes with better performance in high school should not be read as evidence that less sleep is beneficial; it more likely reflects academic pressures in the Korean context.
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Enkhjin T, Ro J, Shin Y, Nhem D. (2026). Associations of Smartphone Use Time and Sleep Duration With Academic Performance Among Korean Adolescents by School Level.. The Journal of school health. https://doi.org/10.1111/josh.70271