OFFICER Craig Davis reckons 2015 was a fairly peaceful year at Furr High School, on the hardscrabble east side of Houston. True, five of its pupils died violently, including the school’s first-pick quarterback, Michael Davis, who was murdered in a gang fight, and two schoolgirls who were killed in a bus crash. In the state that executes more people than any other, a recent old boy was also charged with three murders. Yet Mr Davis, one of the school’s two police officers, with a revolver, canister of pepper foam and a truncheon hanging from his belt, says he has known worse over his eight years at Furr: “It’s a tough place.”

It was with violent schools like Furr in mind that Texas began stationing police officers in its schools in the early 1990s, which helped start a national trend. It proceeded to accelerate on the back of persistent concerns over law and order during the decade; in 1999, after 13 people were massacred at Columbine High School, in Colorado, the federal government launched a supportive funding programme, Cops in Schools. By 2007 an estimated 19,000 school policemen, known as School Resource Officers, were plodding the corridors of America’s schools, in addition to many regular police and private security officers.

How many there are now is unclear; there has been little study of the phenomenon, a gap the Department of Education is struggling to fill. But there may be as many as ever, encouraged by yet more federal largesse in the form of a scheme launched under Barack Obama, in response to yet another school shooting, in Connecticut in 2012, in which 20 children were killed. Most American public high schools now have a permanent police presence.

It is not clear why. Over the same 25-year period juvenile violent crime rose through the early 1990s but, like the overall crime rate, has since collapsed. Juvenile arrests are also at their lowest level for three decades and juvenile murders at a 30-year low. Gone, too, are excited apprehensions of a feral underclass of pre-teenage “superpredators”, a discredited phrase coined by John DiIulio, a Princeton political scientist.

When asked in a national survey, in 2005, why they had brought police onto their campus, only 4% of school principals and the cops themselves cited violence as the main reason. About a quarter of the teachers instead cited media reports of violence elsewhere; a quarter of the cops said the school was unruly. The most popular response was “other”, a category that included the availability of federal funds (what school would not take free money?) or a belief that the policy had something to do with community policing.

Preventing school shootings hardly registered; it is a rare sort of calamity, which, as it happens, the presence of armed officers does not prevent. There was a police officer at Columbine during its massacre. Moreover, such shootings tend to happen in schools dominated by middle-class whites, and according to researchers at the American Civil Liberties Union (ACLU), cops are far more likely to be placed in schools dominated by poor non-whites.

The result, because police like to keep themselves busy, has been a disproportionately high number of arrests in such schools, pitching black and Hispanic juveniles into the criminal-justice system. Of 260,000 pupils referred to the police in the 2011-12 school year, 27% were black, though blacks represented only 16% of the student population. And those who become entangled in the justice system are likely to remain so. The opening of a juvenile criminal record—which may not be scrubbed clean until the age of 21—is an augury of further arrests, further convictions and eventual imprisonment, a spiral known to researchers as the “school-to-prison-pipeline”. “What started as an effort to keep guns out of schools has become a way of getting kids out of school,” says Harold Jordan of the ACLU.

There are several reasons why the policy has gone bad, which vary from place to place. One is uncertainty about who is in charge, police or principals. Sometimes the cops answer to the school board, sometimes only to the police chief. Often the balance of power is contested in an ill-tempered battle between principals and police. The eagerness of weak, or ill-equipped, teachers to outsource classroom discipline to the cops is another part of the problem. This allegedly contributed to a recent much publicised case of police abuse in South Carolina, where a 16-year-old girl was thrown to the floor and dragged from the classroom by a police officer after she had refused to stop using her mobile phone. The internet has plenty more such horrors; including footage of a sobbing 5-year-old girl in Florida, handcuffed after she threw a tantrum.

Draconian laws, inflexibly applied, make matters worse. Until recently in Texas it was a criminal offence to cause a rumpus on a school bus; in South Carolina, it still is one to cause a disturbance in school. In Pennsylvania, among other states, it is a criminal offence to take a weapon, including an almost-harmless pair of nail-scissors, into school, for which even a ten-year-old would face arrest. “It’s the stupidest, craziest thing I’ve ever seen, says Kevin Bethel, Philadelphia’s newly retired deputy-commissioner of police.

After arrest—a fate until recently experienced by around 1,600 students in Philadelphia each year—the arrested child is taken to the district police headquarters for fingerprinting and processing, which takes about six hours, much of it spent in a prison cell. Minor offenders, including weeping ten-year-old scissors-carriers, are then let off with the sort of punishment a teacher might have demanded in the first place, such as lines or chores—though if they fail to carry these out, they may wind up in court, alongside more serious offenders. “What does it mean when we take a ten-year-old child into a cell block and we don’t really know why?” asks Mr Bethel.