And Floyd brushed aside the complaints that the scanners are used primarily in schools serving low-income black and Hispanic students. Children from those neighborhoods, he said, often require them.

“Would I say, put metal detectors in Brooklyn Tech? I would not,” Floyd said, because the students there, “some from affluent neighborhoods,” are “committed to learning, they’re not committed to fighting. That’s not the case in every New York City public school, and you can’t say, ‘Treat the children the same’ because we don’t do that.”

Despite the widespread use of the scanners, the amount of contraband found is low. In the approximately 3 million scans conducted in the first two months of this school year, only a tiny number of contraband items were discovered, according to a NYPD document obtained by ProPublica. Among the 126 possible weapons seized at schools that scan daily—some found hidden on school grounds, others by scanners—were an unloaded handgun, 73 knives, 21 boxcutters, three BB guns, and an assortment of loose bullets and razor blades.

Some school officials believe the daily security checks actually lead to behavior problems among the students. Until recently, Tyler Brewster was a dean of discipline and a math teacher at the School for Democracy and Leadership in Brooklyn, which has metal detectors. She now works at The James Baldwin High School in Manhattan, which does not. Brewster said she doesn’t believe students at either school should be forced to go through the scanners, and that it brands whole groups of students as untrustworthy.

“We didn’t have to go through the metal detectors as teachers, and I’m no less or more human than our students. Why do you trust me to have a bad day and handle it the right way versus the kid having the bad day?” Brewster said. “I wonder how much of the tone is set by having metal detectors in the first place.”

Kamaya Sanders, a student at the Secondary School for Journalism in Brooklyn, said that she sometimes felt suspicious of her fellow students as they stood in line to get checked.

“Sometimes you want to say your school’s safe, but you have the metal detectors, so you never know. Then let’s say someone in front of you gets stopped, then you’re like, ‘Oh, they may have something.’ You get scared,” Sanders said. “It does make you feel safe in a way, but sometimes it’s not worth it.”

At Democracy and Leadership, Brewster said, the scanning led to daily altercations, some of which have ended with arrests.

“There were maybe 3,000 students in my building and every single person had to be scanned,” she said. “On rainy days, the kids were gonna have to wait in line. In some cases, they had to take their shoes off, but the floors were wet so then there would be an argument between the safety agents about not taking their shoes off, and then not being allowed into the building and then that would escalate.”

The dilemma of the scanners is on display at a massive brick building in the heart of Park Slope in Brooklyn. The building, which takes up an entire city block, once housed a single high school, John Jay, with a tumultuous reputation. Now four new schools share the building. One of the schools, Park Slope Collegiate, would like to remove the metal detectors, the others don’t.

Bloomberg, Collegiate’s principal, said the neighborhood, which is now filled with trendy shops and restaurants, has changed significantly and that fights or weapons in the building are now rare.