Active shooter drills are meant to prepare students. But research finds ‘severe’ side effects.

A few things go through Tim Tredwell’s mind when he’s in the middle of an active shooter drill, leading his physical education class into the locker room at John Winthrop Middle School in Deep River, Connecticut. He thinks about which student has a special education plan, whether any of them do not handle trauma well, or if there’s one he’d have to carry if they had to run. He thinks of his own children.

Even when Tredwell knows it’s only a drill, he still feels a jolt of apprehension when the principal comes by to shake his door to ensure it’s locked. It’s been this way since the drills began shortly after the elementary school massacre in Newtown, Connecticut, in 2012.

“It kind of ended the gun control debate,” Tredwell said. “We saw kindergartners get killed and what changed? It’s clearly going to keep happening. So the question became, what do we do when they do?”

He added, “It’s the bizarre nature of where we are as a society.”

Active shooter drills became one of the most common school safety measures implemented nationwide in recent years, despite widespread fears that the procedures heighten anxiety, and evidence that school shooters, like the one in Parkland, Florida, use knowledge of the drills to their advantage. Teachers unions in February called for schools to not conduct active shooter drills with students. Now, new research adds data to those concerns.

A report being released Thursday, obtained in advance by NBC News, found active shooter drills in schools correlated with a 42 percent increase in anxiety and stress and a 39 percent increase in depression among those in the school community, including students, teachers and parents, based on their social media posts.

Authorities in Livingston, Montana, conduct an active shooter drill at Park High School in April 2018.William Campbell / Corbis via Getty Images file

The report, released by the advocacy group Everytown for Gun Safety, relied on research from Georgia Tech’s Social Dynamics and Wellbeing Lab, which analyzed 27.9 million tweets and 1,454 Reddit posts that came from accounts with connections to 114 schools in 33 states that held active shooter drills in the 2018-19 academic year. The researchers examined changes in social media posts in the 90 days before and after a drill. The higher rates of anxiety and depression were evidenced by an increase in words such as “afraid,” “struggling,” “nervous,” “therapy” and “suicidal.”

“It wasn’t just a short duration that everybody shakes off — it’s having a lasting impression,” Sarah Burd-Sharps, Everytown’s research director, said.

This methodology is known as psycholinguistic analysis, and has been used by researchers to examine people’s attitudes over time, such as on college campuses following shootings and during COVID-19 lockdowns.

*story by NBC News