Teens check their phones every hour during school, and the cognitive costs are measurable

JAMA, March 2026

One-third. That is the fraction of the school day that middle and high school students spend on their smartphones, according to a new study that tracked phone use objectively rather than relying on what teenagers say they do.

The research, published in JAMA by a team at the University of North Carolina at Chapel Hill, monitored smartphone activity hour by hour over two weeks, generating thousands of data points per participant. The results offer the most granular picture yet of how phones compete with classrooms for adolescent attention.

Every hour, without exception

The study's most striking finding is the sheer consistency of phone use throughout the school day. Students were not sneaking a peek during lunch or between classes. They were on their phones during every hour of instruction, according to lead author Eva Telzer, professor of psychology and neuroscience at UNC-Chapel Hill.

Social media and entertainment apps accounted for more than 70% of that time. Educational or productivity-related use was a small fraction. The phones were functioning primarily as portals to platforms designed to capture and hold attention, not as learning tools.

Co-author Kaitlyn Burnell, a research assistant professor at UNC-Chapel Hill, noted that the sheer volume of phone use during school hours surprised the research team. The objective tracking data painted a picture that likely exceeds what students themselves would report, a common finding in studies comparing self-reported and measured screen time.

Checking frequency matters more than total time

The study's more nuanced contribution lies in distinguishing between total screen time and checking frequency. Students who picked up their phones more often throughout the day showed poorer performance on measures of cognitive control, the umbrella term for the mental skills that allow people to focus, resist impulses, and shift attention deliberately.

This distinction carries significant implications. It suggests that the interruption pattern itself, the constant switching between task and phone, may be more disruptive than the cumulative minutes spent on screens. Each check represents a break in attention that requires cognitive effort to recover from, a phenomenon researchers call attention fragmentation.

The relationship between checking frequency and cognitive control held even after accounting for total screen time. In other words, a student who checks their phone 30 times for 30 seconds each time may show worse attention outcomes than a student who uses their phone for the same total duration in fewer, longer sessions.

Correlation, not causation, and other caveats

The study is cross-sectional, meaning it captured a snapshot rather than tracking changes over time. It cannot establish whether frequent phone checking causes weaker cognitive control or whether students with pre-existing attention difficulties are simply more drawn to their phones. Both directions are plausible, and the reality likely involves some of each.

The sample size and demographic details were not fully specified in the press release, which limits assessment of how broadly the findings might apply. Cultural and socioeconomic factors that influence both phone access and school environments could shape the relationship between phone use and attention in ways this study may not capture.

The cognitive control measures used in the study reflect laboratory-based assessments. Whether the patterns translate directly to academic performance, grades, test scores, and classroom engagement, remains to be demonstrated through further research.

Policy in motion

The findings land in the middle of an active policy debate. States and school districts across the United States are adopting new phone restrictions, ranging from complete bans during school hours to more targeted approaches that limit access to specific apps or during instructional time.

Telzer frames the data as supporting restrictions on access to social media and entertainment apps during school, rather than necessarily banning phones altogether. This targeted approach would preserve potential educational benefits of smartphone technology while limiting exposure to the platforms most strongly associated with attention disruption.

The question of enforcement remains open. Policies that restrict phone use face practical challenges in implementation, and the study does not address whether restrictions actually improve cognitive outcomes. But it does provide the kind of objective, quantitative evidence that policymakers have been requesting as they weigh increasingly aggressive interventions in the relationship between students and their devices.