KIPP DC KEY Academy Principal John Barnhardt, right, and Vice Principal Rashaand Sass, center, greet students as they enter the building to start their school day Friday in Washington. (Keith Lane for The Washington Post)

The staff at IDEA Public Charter High School greets each child by name every morning. They shake some students’ hands, give others a quick high-five and engage in brief conversations when they can.

The morning ritual is intended to create a warm learning environment. But it’s not all about cordiality: It’s also part of the high school’s safety plan.

Justin Rydstrom, the head of IDEA, said the school banished metal detectors five years ago, believing that staff members who have built a rapport with students are better equipped than any machine to detect if a teenager seems off one day.

“Staff relationships and staff presence really give us our best indicators in terms of what students are coming into the doors with and how they are feeling,” Rydstrom said.

The February shooting that left 14 students and three staff members dead at Marjory Stoneman Douglas High School in Parkland, Fla., intensified the debate over whether metal detectors and X-ray machines that are common in airports and courthouses belong in schools.

Following the shooting, Stoneman Douglas’s school system said it would launch a pilot program with metal detectors at the school during the upcoming academic year. But earlier this month, Broward County Public Schools announced it would delay the plan because of concerns regarding staffing, privacy and logistics — a move that angered parents who wanted enhanced safety measures.

“As we continue our due diligence to implement the program — consulting with vendors and experts . . . — many issues have been raised that require the District to pause and have a more thoughtful discussion on policy and procedural aspects of this pilot,” Robert Runcie, the superintendent of Broward County Public Schools, wrote in a letter to Stoneman Douglas families.

Students in Washington and other urban school districts have encountered metal detectors in schools for decades. In 1991 — when crime rates were higher in the District — the D.C. Board of Education voted to install metal detectors at the front entrances of 10 middle and high schools after a teenage girl stabbed a classmate in the cafeteria of an Anacostia school.

Every middle and high school in the District’s traditional public school system now has metal detectors and X-ray machines. D.C. Public Schools declined to provide details of its security measures. But Shayne Wells, spokesman for the school system, said metal detectors and X-ray machines detect illicit items daily, leading to the confiscation of pepper spray, knives and mace.

But, like IDEA, some schools in the charter sector — which are privately run but publicly funded and educate nearly half of D.C.’s public school students — are opting for a different route. Rydstrom said the machines often inaccurately detect metal objects on students, leading to unnecessarily invasive searches. He said that students should arrive at school early, eat a healthy breakfast and go to class, and that metal detectors slowed morning arrival.

School security officials at IDEA check students’ bags and use a security wand to determine if students are carrying weapons, but Rydstrom said he hopes to move toward a randomized security process.

Chris Dorn, a senior analyst at the school security consulting firm Safe Havens International, said that while more school districts are discussing metal detectors and X-ray machines, few are moving to install them.

About 3 percent of the country’s public schools report having students walk through metal detectors daily, according to a study on school safety released in 2016 by the Rand Corp., a think tank.

Dorn said that parents are often behind pushes for more security but that metal detectors can be expensive and impractical — and don’t necessarily increase safety.

In suburban campuses with thousands of youngsters, students often have their choice of entrances. Schools would have to pay for multiple metal detectors and X-ray machines — and hire trained staff to run them — or have students arrive through a single entrance.

Dorn said school shootings are at the root of much of the anxiety surrounding school safety. But metal detectors, he said, will not protect students from shooters intent on killing many people or harming themselves — scenarios that Dorn stressed remain rare.

And when monitoring for weapons at schools, Dorn said, the machines are not infallible.

In 2015, a student at Woodrow Wilson High School in Northwest Washington managed to enter the school, which has metal detectors and X-ray machines, with a semiautomatic handgun and flashed it in the hallway later in the day.

“Most people have a lot more anxiety, and we need to make sure not to overpromise,” Dorn said. “It’s a bad thing to imply safety when it’s not legitimate.”

Shanese Bryant, a mother of a 10th-grader at Cardozo Education Campus in Northwest Washington, said she is comforted knowing that her son’s school has a metal detector, hoping its presence ensures that students are not bringing weapons into classes.

“It makes me feel more comfortable,” Bryant said, “knowing that they can detect something before anything happens to the children.”

At KIPP DC KEY Academy in Southeast Washington, school leaders have also opted against metal detectors. John Barnhardt, principal of the charter middle school, said people perceive metal detectors as evidence that a school must be violent or “bad.”

Barnhardt, who is working on a dissertation exploring school safety, said that his students come from neighborhoods with high crime rates and that he wants them to enter campus feeling welcome.

Students at KIPP receive greetings in the morning from unarmed security guards and administrators. The school is staffed with social workers and psychologists, so if someone senses something is amiss with a student, mental-health workers can quickly intervene.

Metal detectors “can set the expectation that we think they are violent,” he said. “It’s tough because we can never completely know a student, but I do think that KIPP DC has made a significant investment in the social-emotional aspect.”