High school biology teacher Kelly Chavis knew smartphones were a problem in her class. But not even the students realized how much of a problem the devices were until Chavis did an in-class experiment.

　　For one class period, students used a whiteboard to count every Snapchat, Instagram, text, call or other notification that appeared on their phones. Chavis told students to not respond to these notifications.

　　Teachers around the country have done similar experiments, usually recording dozens of markings on the whiteboard.

　　Chavis, who teaches honors-level classes at Rock Hill Schools in South Carolina, was shocked by the results of her experiment.

　　"One girl, just during the one hour, got close to 150 Snapchat notifications. 150!" she said.

　　Chavis is among a growing number of teachers, parents and health experts who believe that smartphones are now partly to blame for increasing the levels of student anxiety. The use of electronic devices is so widespread that the National Education Association newsletter said it was a "mental health tsunami."

　　Tests, after-school activities and problems at home can increase stress for students. But research now suggests that smartphones and social media are some of the main reasons for the rising anxiety levels.

　　Jean Twenge is a psychology professor at San Diego State University in California. Twenge said it is not a coincidence that youth mental health issues have risen with the number of phones. "What a lot of teens told me is that social media and their phones feel mandatory," she said. This use of phones has led to a loss of sleep and face-to-face interactions necessary for their mental well-being.

　　Last year, an editorial in the journal Pediatrics proposed that doctors ask young patients about their social media use as part of routine exams. Three researchers wrote that too much social media use might "contribute to the development of mental health disturbance in at-risk teenagers, such as feelings of isolation, depressive symptoms, and anxiety."

　　Researchers are still not sure whether phones cause student depression or depression causes phone use. Yet 70 percent of teens see anxiety and depression as major problems among their peers, according to a February Pew Research Center report.

　　Nearly 60 percent of parents said they worry about the influence of social media on their child's physical and mental health. That number comes from the American Psychological Association's 2017 Stress in America survey.

　　Schools are starting to take steps to deal with the problem. Many public schools pay outside companies to watch students' social media activity for signs of distress. Others invite in yoga teachers and comfort dogs to help calm students.

　　Some schools have organized #unplugged events – days in which people do not use their electronic devices. Belfast Area High School in Maine had one such event in April. Less than 20 percent of students and school employees took part, demonstrating the influence that the technology has on their daily lives.

　　Emily Mogavero is a 17-year-old student in Buffalo, New York. "I definitely feel stress with online profiles, social media, to keep up, maintain my profiles and stuff," she said. "It kind of worries me that I'm on my phone so much." Mogavero said she sometimes puts her phone out of reach or powers it down so she doesn't hear notifications.

　　Some parents are not letting their children get smartphones until they grow up. Western New York yoga teacher Erin Schifferli says her 12-year-old daughter, Aeva, won't get a phone until she is 16 years old.

　　Deirdre Birmingham of Montclair, New Jersey, signed onto a campaign called "Wait Until Eighth" because she didn't think her video game-loving 10-year-old son was ready for a smartphone. The campaign joins groups of parents who have children in the same class. These parents agree to not let their children get phones until they are teenagers, or in the 8th grade.

　　Birmingham said she had a feeling that the phone "would be difficult for my child to manage....As a grown-up, I find it difficult sometimes to manage."

　　I'm John Russell.

　　And I'm Ashley Thompson.

　　The Associated Press reported this story. John Russell adapted it for VOA Learning English. George Grow was the editor.