Teens check their phones up to 144 times during school; and it may affect cognitive control

By Dr. Liji Thomas, MDReviewed by Lauren HardakerMar 13 2026

Hour-by-hour smartphone tracking reveals how deeply phones are embedded in the school day. Some teens checked their phones more than 140 times, with frequent checking linked to weaker cognitive control.

Study: Smartphone Use During School Hours and Association With Cognitive Control in Youths Aged 11 to 18 Years. Image credit: Ground Picture/Shutterstock.com

A study published in JAMA Network Open found that adolescents frequently use smartphones during the school day, and frequent phone checking was associated with poorer cognitive control. Some students checked their phones more than 140 times during school hours, with the highest count at about 144, according to the study.

Why adolescent brains are vulnerable to smartphone distraction

Smartphones are part of everyday life for modern adolescents. However, they can be sources of distraction and hinder academic engagement and self-regulation. Adolescents are especially prone to distraction, as the brain areas involved in cognitive control are still maturing, while sensitivity to social rewards is high. Cognitive control refers to the goal-directed regulation of emotions, thoughts, and behavior.

Earlier studies showed high screen time, mostly on social media, among adolescents, but did not specify specific times of day. They also suggest that older students have increased screen time during school hours compared with younger students. The authors propose that this is due to weak self-control, leading them to prefer the immediate gratification of social media or entertainment to the delayed reward of achieving their goals - in this case, academic achievement.

Other scientists theorize that smartphone use causes distraction by interfering with other attentional foci or by depleting cognitive resources used for attention. Previous research has demonstrated that frequent smartphone checking is a more reliable indicator of habitual smartphone use than overall screen time. This has also been correlated with altered activity in the prefrontal cortex, the region involved in cognitive control.

This prompted the current study, which examined smartphone use during school hours by middle school (11-14 years) and high school (15-18 years) students, and whether smartphone use during school hours was associated with weaker cognitive control.

Tracking hourly smartphone use over 14 days 

The study involved 79 youths with a mean age of 15 years. This cross-sectional study used Apple’s iPhone iOS screen time reports to objectively capture smartphone use each hour for 14 consecutive days per participant. Middle school students had to upload three screenshots each day, reflecting the prior day’s use in three metrics: overall screen time, social media, and entertainment. For the older students, the metrics were: overall screen time, pickups, and notifications.

Different metrics were requested across groups to provide a broader picture while reducing the tasks required of the participants, thus maximizing adherence. In addition, cognitive control was evaluated with a go/no-go task designed to measure inhibitory control in the older high school cohort.

Study findings

Total smartphone use

The investigators found that all participants used their smartphones during school hours, for periods ranging from eight minutes to 5.3 hours. Smartphone use occurred every hour of the school day, totaling 2.2 hours, or one-third of the school day. This comprised 28.5 % of total smartphone use over 24 hours.

The total use time doubled from a mean of 12 minutes in middle school students to 23 minutes in the high school group. Screen time among younger children was greater on non-school days than on school days, suggesting a possible inhibitory effect of school structure, in contrast to older adolescents.

This may signal that older adolescents tend not to restrict their smartphone use compared to younger teens, suggesting that smartphone-related autonomy may interact with adolescent development in self-regulation and social behavior. Alternatively, the researchers suggest that the younger cohort, evaluated two years later than the earlier cohort, showed the effects of tighter regulation of smartphone use in school hours. Other factors might include parental regulation and the effect of monitoring. This requires further research.

Social media and entertainment

Middle school participants spent an average of 40 minutes on social media and 14 minutes on entertainment apps during school hours. Individual durations ranged from zero to about three hours and 1.8 hours, respectively. On average, social media and entertainment made up over 70 % of total school-day screen time, corroborating earlier research. This may indicate powerful engagement with, and immediate but variable rewards from, social media interactions.

This could fuel compulsive behavior, conditioning adolescents to pursue continuing stimulation. This is in contrast to the sustained attention required to obtain the delayed reward of academic engagement.

Phone checking

In the high school cohort, phones were checked every hour, averaging 64 times over the school day, with the highest being about 144. Youths who checked their phones more often were more likely to show lower cognitive control on testing. However, total screen time during school hours was not associated with cognitive control in this study.

The authors relate this finding to theories of attentional fragmentation and cognitive load. Repeated phone checking can lead to frequent task switching, depleting the cognitive resources required for goal-directed behavior. In addition, frequent phone pickups may divert attention, preventing engagement with learning and social activities. Previous research supports this hypothesis, showing that greater social media engagement is associated with poorer cognitive outcomes. Similarly, repeated distraction is linked to executive control.

Finally, problematic social media use is associated with poorer scores on inhibitory control tasks. According to the authors, the relationship may be bidirectional, with reciprocal associations between low self-regulation and frequent smartphone checking during school hours.

Reasons for frequent phone checking remain unknown

The study is limited by its small sample size and the two different periods of data collection. Moreover, only iPhone users were eligible. The categorization of phone use was based on the App Store’s built-in software and may have introduced some misclassification errors.

The study could not determine whether phone use occurred during instructional time, breaks, or lunch periods. The reason for repeated phone pickups was not obtained, and may have ranged from checking the time to checking social media. The study data predated state-level smartphone bans in schools.

Schools may need policies targeting habitual phone checking

The authors say that this study is among the “most detailed, naturalistic accounts of smartphone use during school among youths aged 11 to 18 years.” The findings suggest that all students are involved with their smartphones throughout the school day, rather than just at breaks.

More frequent phone checking during school hours is linked to poorer cognitive control. The authors comment, “These findings highlight the need for school-level policies and digital literacy programs.” They emphasize that youths need help not just to cut down their total screen time, but to reduce the frequency of use, to promote normal adolescent cognitive and social development, and well-being.

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