Parents in the Penn-Delco School District flooded Sun Valley High School with phone calls Tuesday and rushed to pick up their children as rumors spread that something violent might happen.

In Bristol Borough, three students were arrested last week for making three shooting threats in as many days, causing school closings, early dismissals, and heightened anxiety among parents and students.

And on Friday in Cheltenham, the high school’s principal informed parents that police were investigating a message on a bathroom stall threatening a school shooting on Dec. 17. A week earlier, the district had brought in police after discovering a social media post depicting the high school’s floor plan with circled exits.

Such scenes have been playing out across the Philadelphia region and nationally. Schools are chasing a stream of threats — many fueled by social media — that often don’t materialize. But in the process, students and parents are left on edge, unsure how to feel about attending school.

“These are teenagers. They know what happened at Oxford,” said Amanda Scott, a parent in the Penn-Delco district, referring to the recent school shootings in Michigan. Her husband rushed to pick up their son from Sun Valley High after he texted during a lock-in Tuesday that there was a possible shooting threat and he wanted to go home.

“Ten minutes go by, 15 minutes go by — they’re like, ‘Is this the one?’” Scott said.

School administrators see a variety of reasons for the recent wave of threats, the reports made by students, and the panic that followed: A heightened reliance on social media. Fear in the wake of the Michigan shootings — and determination not to let a similar tragedy happen here. And social and emotional needs that may have gone unmet during the disruption of the pandemic.

Dewey Cornell, a forensic clinical psychologist and University of Virginia professor whose Student Threat Assessment Protocol is used widely in the United States and Canada, said he’s hearing from districts around the country that there’s been a “surge of student threats,” many of them coming from social media and possibly part of a “contagion effect of copycat threats following a highly publicized incident.”

But he sees a problem that was present before the Michigan shootings: “A general increase in student anxiety, distress, and misbehavior in school,” said Cornell, who directs the Youth Violence Project at the University of Virginia. “We also have schoolteachers and counselors who are understandably fatigued, short-handed, and less able to respond to student challenges. Schools are under tremendous strain.”

In Philadelphia, where children are living amid a gun violence crisis, the School District has used its threat assessment protocol more than 50 times so far this year. That’s a lot, even for a large school system like Philadelphia’s, said Kevin Bethel, chief safety officer for the district.

On Monday, the district’s Carver High School of Engineering and Science locked down after someone posted a photo of multiple guns on Instagram and promised to “shoot up carver high school on Norris st and berks today at 2:00.” District safety personnel, Philadelphia police, and investigators from the police’s homeland security department who are trained in data mining all responded. No shooting happened.

With social media so prevalent among children — and a lifeline for many in Philadelphia and other school systems where children learned virtually for a year or more — “that does create a challenge, particularly for law enforcement and school safety and school leaders,” Bethel said. “There’s so much activity.”

Word of threats sometimes spreads faster on social media than schools have been able to respond. Some students at West Chester East High School stayed home Wednesday after awakening to text messages and social media posts warning of a threat at the school. Others asked parents to pick them up early.

The warning stemmed from a social media post by a student the night before, announcing a “legal threat against the school.” Police investigated and determined overnight that it wasn’t violent.

But “you put the words school and threat together, and it took on a life of its own,” said Superintendent Bob Sokolowski, whose district investigated two more threats last week: a message in a bathroom stall at Peirce Middle School discovered later Wednesday, and reports Thursday night of a student planning to bring a weapon to Rustin High School. Both were unfounded.

He said he understood the impulse to report. “Parents and students are concerned right now: ‘Is my school going to drop the ball?’”

In Penn-Delco, Superintendent George Steinhoff said he saw a “culmination of the trend that’s happening around the country” last week: On Monday, the high school was disturbed by students fighting in the hallways, in a scene that was later widely viewed on social media. Then on Tuesday morning, a student came forward to report that she had seen a written threat the day before.

The district immediately began investigating and went into lockdown. The threat ended up not being credible, but there was just enough time for students to begin to worry, Steinhoff said. With so many students texting their parents and leaving, the high school ended up dismissing early.

“In some ways, it’s an incident that was created from essentially a non-incident,” Steinhoff said. “It’s a sign of how the heightened anxiety of students right now can make these situations much more difficult to handle.”

Scott, the Penn-Delco parent, felt the school had unfairly blamed students for turning to text conversations or social media when they heard rumors of a threat.

“The one time something happens — that would be devastating,” Scott said.

Steinhoff said there was “a fine line between making sure you’re supporting students” while also trying to maintain order. He plans to hold a webinar for parents Monday and also wants to hear from students about their needs.

“There’s no question that this national crisis in adolescent mental health is manifesting itself in schools,” he said.

This fall, Upper Darby schools have imposed only one actual “lockdown,” which involves darkening lights and can only be lifted by police, Superintendent Dan McGarry said. But “lock-outs” or “lock-ins” that either restrict outside access to the school or keep students from moving between classrooms have been more frequent. The high school, for instance, briefly went on lock-in Friday after a “message was sent to a printer located in the school about causing harm to the school,” district officials said. Police determined it was not an immediate threat.

Earlier Friday, the district informed the community that a social media post circulating among students with the words HHS Shooting written in a bathroom referred to a district in another state. The high school was also on lock-in Thursday after a student showed administrators a social media post with a picture of a person holding a weapon and making a threat toward the student.

Assessing the various threats is “not as simple as people want to make it out to be,” in particular with social media, McGarry said, where it might not be clear when or where a photo was taken.

McGarry said Upper Darby is holding trainings and also disciplining students involved in making threats to “the fullest extent.”

In Bristol Borough, police filed criminal charges against all three students who made threats last week — two high school students and a sixth grader — even though the students didn’t have access to firearms.

“Kids just want to feel safe when they come to school to learn,” said Bristol Borough Police Sgt. Joseph Moors. “I want the parents and students to know that people will be held accountable for their actions.”

Still, administrators see challenges: Social media isn’t going away. And schools have to get to the root of issues driving some students to make threats, said Bethel, the Philadelphia safety officer.

“Whether we arrest them or not, he or she is not going to be expelled from the system,” he said. “We have to be able to do the long-term management of the child’s mental health.”