In schools across the country a troubling scenario is playing out: a call comes in about a shooting at the school. Someone has a gun. Police respond, only to discover the report was a hoax.

Just this week more than a dozen schools in Minnesota were targeted with “swatting” incidents, reports of a false shooter or mass casualty event. Threats in Denver forced the city to shut down all 25 of its public library branches, and an area high school to cancel classes Wednesday amid a surge of hoaxes reported at schools across the state. A Texas teen was arrested for calling in a fake threat to a campus as a “joke,” prompting a warning from Fort Worth police against school hoaxes.

The calls are part of a trend that is disrupting school days, prompting lockdowns and further traumatizing communities already on edge. Although these threats are fake, the menace of real violence looms just months after a gunman killed 19 students and two teachers at an Uvalde, Tex., elementary school.

“It’s really indicative of how people have weaponized the fear that we have about an active shooter against us,” said Amy Klinger, director of programs and a co-founder of the Educator’s School Safety Network, which has tracked violent incidents at schools.

Schools in 14 states – Arkansas, California, Colorado, Florida, Georgia, Illinois, Kansas, Minnesota, Missouri, Oklahoma, Oregon, Tennessee, Texas and Virginia – have reported swatting incidents since Sept. 13, according to the national group of school resource officers. At a school in San Antonio, a man reportedly injured his arm trying to break a window at a high school that went on lockdown after false reports of a shooting this week.

Louisiana has also been affected, with at least 15 schools receiving calls of active shooter threats or mass casualties Thursday. The reports came from an internet-based phone number with an out-of-state area code, officials said.

These calls strain police resources, said Mo Canady, executive director of the National Association of School Resource Officers. Swatting “triggers what should be a very critical incident response from law enforcement, from other emergency services, from the school – that is a lot of resources, time being taken up,” he said.

The FBI is aware of the calls and “takes swatting very seriously because it puts innocent people at risk,” the agency said in a statement. It added it does not have “information to indicate a specific and credible threat” and is working with local, state and federal law enforcement to gather information. The agency did not answer questions about who might be making the calls and if they are connected.

In Washington, D.C., on Tuesday, a report of an active shooter at Roosevelt High School prompted a large police response, but police said the report turned out to be false.

“The caller stated there was an active shooter inside the school and provided specific information to suggest there were multiple students that had been injured, and that somebody was armed with a vest and a gun,” said Dustin Sternbeck, a Washington, D.C., police spokesman.

The school went into lockdown, Brandon Eatman, the school’s acting principal, wrote in a letter to families. The entire ordeal – from the time Eatman said he was informed about the incident to the time police finished canvassing the school’s grounds – took nearly an hour out of the day.

Yolanda Anderson, who has two teenagers at Roosevelt and is president of the parent-teacher association, said she heard about the threat from another parent. She immediately texted her kids. She later spoke to a social worker who said some students were crying, and adults were visibly shaken. The situation has been frustrating, Anderson said, adding she thinks swatting has gained popularity on social media.

“That is what makes me angry,” Anderson said. “The fact that students, or kids, or people on TikTok believe that it’s humorous to cause a waste of tax dollars, to cause unnecessary trauma.”

The possible perpetrators are wide ranging and could include disgruntled parents, students, former employees or random people on the internet who think causing a law enforcement response to that degree is funny, says Klinger, of the national school safety group. School systems often don’t have time to investigate how credible a threat is, because their first job is to secure students, she said.

In Virginia on Monday, an unknown individual called 911 to report an active shooter event at Loudoun Valley and Loudoun County high schools, according to a message from the school system to families. School resource officers and patrol officers quickly investigated and determined the reports were false. Police investigated similar calls of false threats reported at schools in Arlington, Va., and almost 10 other Virginia school systems.

These fake threats being investigated in grade schools follow high-profile bomb threats that have targeted historically Black colleges and universities since January. At least 36 HBCUs – more than one-third of the country’s historically Black schools – received threats this year. Howard University, in Washington, D.C., has been targeted on eight occasions, Wayne A.I. Frederick, the school’s president, said in August.

In a message to the Howard campus, Frederick encouraged professors to give students reprieve, noting “anxiety, interrupted rest, and other factors that can stem from this kind of traumatic experience.”

None of the threats targeting HBCUs have led to actual violence.

Students have just endured more than two years of a pandemic, virtual learning “and just the overall rise of violence in our communities,” said Canady, of the school resource officers association. “To add a false report of a critical incident on top of that and further traumatize them is criminal.”

The Washington Post’s Peter Hermann contributed to this report.