The Philadelphia School District moved last month to mandate the use of metal detectors and X-ray equipment in all of its high schools. But the compulsory use of scanning equipment is far from universal in Philadelphia, or even in big-city school systems around the country.

Thousands of the city’s public high school students aren’t bound by the order. They attend one of Philadelphia’s 32 charter high schools, and for many of those schools, it’s a point of pride that they don’t scan students.

Metal detectors “assume the worst in kids,” said Jim Higgins, CEO and principal of Multicultural Academy Charter School, which educates 275 students in Hunting Park. “There’s never been a serious push for it from our school community. We’re just such a small school, there’s a presumption of goodwill among all, and we’re just reluctant to ruin that.”

Among the city’s 32 charter high schools, that’s a common sentiment. (Of the 32, 11 said they did not use detectors, one said it did, and the rest did not respond or declined to answer.)

The School District said it had student safety in mind when mandating metal detectors and X-ray scanning equipment. For the 2017-18 school year, three guns, five BB guns, and 87 cutting instruments were found and confiscated at district schools, spokesperson Lee Whack said.

Nationally, just 4 percent of public schools use metal detectors, according to the National Center for Education Statistics.

Fewer than 100 of New York City’s public schools have permanent metal detectors; Miami public schools employ random metal detection. In Los Angeles, all middle and high schools are directed to carry out daily searches of random students, though a blue-ribbon panel said the practice was unproductive and recommended discontinuing searches until an audit could be conducted.

Researchers say metal detectors are not an especially effective strategy for preventing violence.

“Metal detectors detect metal,” said Beverly Kingston, director of the Center for the Study and Prevention of Violence at the University of Colorado. “They don’t necessarily prevent violence. If you want to prevent violence, there’s a lot more effective, evidence-based strategies, and we recommend using them.”

Among those strategies are creating positive school cultures and making sure schools have effective threat-assessment processes in place, Kingston said.

Kenneth Trump, a school-security expert, said that metal detectors are “no panacea” and are often deployed after school shootings or stabbings as “security theater” — a visible symbol to concerned parents that leaders are concerned about safety. In reality, Trump said, metal detectors do not offer “that 100 percent guarantee that you want. The number-one way we find weapons in schools is not through a metal detector; it’s through students coming forward and telling adults that they trust.”

The Philadelphia School District first purchased metal detectors for some high schools at Superintendent Constance Clayton’s behest in 1992, after one student shot another at South Philadelphia High School. Metal detectors and X-ray scanning equipment were given to all high schools in 1999, in the aftermath of a student shooting an assistant principal inside Bartram High School.

The backlash was swift. A few months later, more than 100 students from Masterman, the elite Center City magnet, marched from their school to district headquarters, holding signs that read: “City kids get metal detectors. Suburban kids get counselors.”

Similar themes are being echoed now. Youth opposed to the policy made their feelings quite clear at a school board meeting last month, bitterly decrying the culture of mistrust they said scanning equipment creates and ultimately disrupting the proceedings out of anger. They said metal detectors criminalize students and further the school-to-prison pipeline.

Though charters operate with public money, they are privately run and so are free to make their own calls about whether to use metal detectors.

The Mathematics, Civics, and Sciences Charter School on North Broad Street does have security measures, founder and chief administrative officer Veronica Joyner said, including cameras and security personnel, including “parents and other people who care” stationed at doors, in hallways, and outside the school at dismissal time.

“Everybody knows they’re responsible for safety, even the students, teachers, and office staff,” Joyner said, adding that “if you set up the right culture in the school, it’s not snitching, it’s reporting.”

For some schools in neighborhoods where crime is common, the choice to not use detectors is deliberate, but not without risk, one operator said. The charter official said his school does not regularly use metal-detecting equipment but asked not to be named because he feared telegraphing the school’s lack of equipment might “make us a target to the unstable element that might be out there looking to make a point or meaning to do harm to others.”

The school, the official said, relies on relationships to keep students safe.

“Combined, in my opinion, these contribute more positively to safety and a conducive learning environment than metal detectors,” said the administrator, who believes that whether a school has metal detectors “has long-term implications on kids and how they view the norms of their working and living environments.”

For some charters, there are logistical issues to consider. At MaST, a K-12 school in the Northeast, there are no detectors — and students use a single entrance.

“You’d have to have everybody go through it,” said John Swoyer, the school’s CEO. While “I don’t think we would take anything off the table,” moving over 1,000 elementary, middle, and high school students through scanning equipment would be a challenge.

Some charters do opt to scan students. At Preparatory Charter School, a high school in South Philadelphia, metal detectors and screening equipment have been in place for three years, said Chuck Pearsall, the school’s head of security.

The school wanted "an extra layer of protection” based on “the climate with regard to school shootings, lockdowns, and intruders,” Pearsall said. The school started with one metal detector, then added a second and an X-ray machine.

Students who may be running late and get caught up in the screening process “get a little aggravated” with the scan, Pearsall said, but he said he had not heard complaints that the security measures were a bad idea.

Pearsall said he was not at liberty to disclose whether students had brought weapons to Prep Charter. But asked whether he thought detectors have served as a deterrent, he was unequivocal.

“Without question,” he said.

The School District has said that it will hold discussions on how scans are carried out now and how that affects students, and that it will require employees who scan students to undergo training.