A new study published in JAMA Network Open on March 9, 2026, reveals a striking and troubling pattern: teenagers are spending more than 2 hours a day on their smartphones. Led by Dr. Eva H. Telzer and researchers from the University of North Carolina, Chapel Hill, the findings paint a clear picture of how habitual smartphone use during school hours directly fragments attention spans and weakens impulse control in adolescents. These results add significant weight to a growing body of evidence that excessive screen use is reshaping how young people think, learn, and function.
How the Study Was Conducted
Researchers studied 79 teens ages 11 to 18 from the Southeastern United States, assessing smartphone use over 14 consecutive days across two time periods — from April 2021 to February 2022, and again from February 2023 to December 2024. Rather than relying on self-reported estimates, which are notoriously unreliable, the research team used Apple iPhone iOS screen time reports to capture smartphone use at every hour of the day, generating thousands of data points of actual engagement. They also measured cognitive control alongside screen time data.
The Numbers Are Hard to Ignore
The data produced some eye-opening statistics. Students spent one-third of their school day using smartphones, averaging 2.22 hours of total smartphone use per school day. Roughly 70 percent of that time was spent on social media or entertainment apps.
Perhaps even more concerning is the frequency of phone checking. Teens checked their phones 64 times during school hours, and those who checked more frequently were more likely to score lower on cognitive function and show indicators of poorer cognitive control. Age also played a significant role in usage levels. Older teens aged 15 to 18 spent considerably more time on their smartphones during school than their younger peers aged 11 to 14, averaging 23 minutes per hour, compared to just 11 minutes per hour for the younger group.
Why the Brain Is Especially Vulnerable
The implications of this research go beyond grades and test scores. Researchers say these risks may be amplified by platform features designed to maximize engagement — such as algorithm-driven feeds, autoplay videos, and infinite scrolling. Adolescents are considered particularly vulnerable because developing brains are more sensitive to social feedback and reward-based stimuli. In other words, the very design of these platforms exploits the natural neurological vulnerabilities of teenage brains, making compulsive checking not simply a bad habit, but a deeply ingrained behavioral response.
This connects directly to what mental health professionals have observed in clinical settings. Health experts have long warned that excessive smartphone and social media use may harm child development, increasing risks of anxiety, depression, sleep disruption, and feelings of isolation. Some research has also linked heavy social media use to increased suicide risk among adolescents. A related study published in February found that teens who spend more than 16 hours per week on social media — roughly two hours per day — face a significantly higher risk of loneliness and depression.
What the Researchers Are Recommending
The study’s authors were clear about who was responsible. Researchers concluded that frequent smartphone use can impact learning and cognitive development, and they emphasized the need for school policies to address screen use, as well as programs to improve digital literacy and reduce habitual smartphone-checking behaviors. This is a call not just for stricter rules, but for education — teaching young people to understand what these platforms are doing to their attention and behavior, and giving them the tools to push back.
The Legal Landscape Is Catching Up
This research arrives as the legal system begins to hold social media companies accountable. Social media platforms currently face more than 2,300 lawsuits pending in the Northern District of California, with the first two federal social media addiction bellwether cases scheduled to go to trial in the summer of 2026. The complaints allege that addictive algorithms knowingly designed by TikTok, Meta, Snap, and Google to maximize user engagement have encouraged compulsive use and contributed to serious mental health problems among children and young adults, including loneliness, depression, eating disorders, suicide attempts, and completed suicides.
Takeaway
This study makes one thing unmistakably clear: smartphones in schools are not a neutral presence. They are actively competing with education for the attention of developing minds — and they are winning. For parents, educators, and mental health professionals, the data is a call to action. School phone policies matter. Digital literacy education matters. And the conversations we have with young people about why these platforms are built the way they are — and what they are doing to the brain — matter enormously. The technology industry has designed these tools to be as engaging as possible, with little regard for the cognitive cost to children. It is now up to families, schools, and policymakers to set the boundaries that protect them.
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