But none of the extensive preparations stopped the rampage of an 18-year-old gunman who entered a primary school in Uvalde this week and killed 19 children and two teachers. Family members who rushed to the scene said they begged the officers, who were gathering outside the school, to enter the building.

The carnage has renewed a decades-old debate over how to end the horror of US school shootings, with many Texas political leaders again calling for tougher school security measures. But others, pointing to the devastation even on campuses that have invested heavily in security, said such a focus could not prevent a hired killer from gaining access to weapons – and that such efforts could in fact give a false sense of security in the absence of firearms. controlling regulations and more robust investments in mental health.

After the 1999 Columbine High School shooting, Congress began providing federal dollars to campus officers, and officials established — and redid — security protocols inside schools, lockdown training drills to elaborate identification requirements. Nationally, 19% of elementary school students, 45% of middle school students, and 67% of high school students attend a school with a police officer on campus, according to a 2018 report from the Urban Institute.

Yet there is little evidence nationally that dollars poured into school safety measures have reduced gun violence in schools, according to a 2019 study co-authored by Jagdish Khubchandani, professor of public health at New Mexico State University.

“These safety measures are not effective,” Dr Khubchandani said this week. “And they’re not catching up with the ease of access with which people are acquiring firearms during the pandemic.”

The nationwide epidemic of school shootings has only worsened, sometimes in situations where armed school officers were present. A duty officer at Marjory Stoneman Douglas High School in Parkland, Florida, in 2018 was charged with going into hiding while a gun-toting teenager killed 17 people.

After a shooting at a high school in Santa Fe, outside of Houston, left 10 dead in 2018, state leaders have pushed for new plans to bolster school security. Plans focused on detecting mental health conditions, expanding social media threat monitoring, training on shootings and increasing law enforcement presence in schools. Statewide, $100 million has been budgeted for security upgrades such as metal detectors, security systems, two-way radios and bulletproof glass.

Uvalde, a small community not far from the US-Mexico border, was among the beneficiaries, securing a $69,141 grant.

Around the same time, the school district was implementing its own security. He hired two new police officers last year, growing to a six-person force that serves around 4,000 students at several schools. School system spending on security and surveillance services has more than doubled in the past four years, according to budget records.

The district’s security plan included two-way radios, threat assessment teams at every school, and a locking policy on every classroom door. At Robb Elementary, where the rampage took place on Tuesday, officials described fencing surrounding the campus that was “designed to limit and/or restrict access to people without needing to be on campus,” according to records. of the district.

The school district’s safety training drills in August 2020 included its own police officers, the Town of Uvalde Police, the County Sheriff’s Office and other local agencies.

“It was very successful,” School District Police Chief Pete Arredondo wrote in a summary for district officials.

School district officials did not respond to messages seeking comment Thursday.

Details of the massacre inside Robb Elementary School were still emerging, but officials provided a timeline of events in which they said a school district police officer surrendered at school after 911 calls came in around 11:30 a.m. Tuesday. After the officer arrived, the shooter — who had scaled a fence to enter the parking lot — fired into the school and then entered it, according to the timeline. At one point, at least two members of the Uvalde Police Department entered the school, officials said, but were shot and retreated.

About 90 minutes after the initial 911 calls, officials said, U.S. Border Patrol officers entered the building and killed the shooter.

Since the Columbine High School murders more than two decades ago, law enforcement training in shooting situations has evolved significantly. At the time, the focus was on making sure officers secured a perimeter before moving in. Agents are now trained to neutralize a shooter as quickly as possible, without waiting for the arrival of a tactical team or special equipment and before rescuing victims.

The approach changes if the gunfire stops, as was the case in the Pulse nightclub shooting in Orlando in 2016, when the shooter barricaded himself in the bathroom with several victims. Barricaded hostage situations can be complex. During the shooting at the nightclub, the shooter, on the phone with crisis negotiators, claimed he had explosives. At the same time, injured victims needed treatment. When officers broke through a bathroom wall, the shooter resumed shooting.

Mo Canady, executive director of the National Association of School Resource Officers, said school officers had prevented many instances of violence that did not attract attention. He mentioned a National Policing Institute database that showed 120 cases of school violence avoided between 2018 and 2020.

Mr. Canedy said his organization had trained several Uvalde school officers over the course of four years, but they were generally based in high schools, not elementary schools. He cautioned against jumping to conclusions about officers’ actions on Tuesday.

Storming a building too quickly could allow a gunman to escape, he said. And while capturing or killing a gunman is a “plan A,” he said, containing the person in a particular space can be an effective “plan B” to mitigate the carnage.

The Texas Rangers are investigating local police’s response to the shooting as part of a larger investigation into the massacre, state officials said Thursday.

The Uvalde School District, like many others across the country, also used measures related to student well-being in its efforts to prevent violence, documents show. The district used software called Social Sentinel, which monitors students’ social media posts for threats, and an app called STOPit, which allows anonymous reports of bullying.

Ron Avi Astor, a school violence expert at the University of California, Los Angeles, said that while emotional supports have greatly improved the school climate, these strategies – along with the presence of police officers from the campuses – have been insufficient to prevent suicides, deeply troubled young men from carrying out attacks.

The focus, he said, should be on referring high-risk people to mental health treatment while preventing them from buying or owning guns.

“We have to start talking about shooters and shootings differently,” he added.

Like schools in Uvalde, most schools in the United States are holding lockdown drills. While some survivors of last year’s shooting at Oxford High School in Michigan credited the formations with helping them escape the building quickly, there’s little evidence the drills mitigate the risk – and plenty of parents, educators and mental health experts worry that they are causing fear and anxiety in children.

There are simple, inexpensive measures that are protective, say those who have studied school shootings. One of them is to keep the doors of the classrooms locked, which was a requirement of the district of Uvalde.

It is unclear whether this practice was being followed at Robb Elementary on the day of the shooting. The shooting happened after an awards ceremony, when relatives said they walked in and out of the building.

The Uvalde District Safety Plan also outlines the use of the Raptor visitor management system, which scans visitor IDs and checks them against sex offender registries and non-custodial parent lists.

At a news conference in Uvalde this week, Lt. Gov. Dan Patrick praised the district’s safety measures, but suggested limiting schools to one entrance was an improvement worth considering.

Officials in Georgia and Virginia have deployed additional officers to schools as a precaution, and Senator Ted Cruz of Texas suggested to put more armed police in schools. New York City, the nation’s largest school district, said it would consider locking school doors after students arrive for the day. Los Angeles said it would reduce entry points for schools.

But Dr Khubchandani wondered if any of these measures would stop a future shooter.

“It’s like heart attack medicine while still eating badly instead of eating healthy,” he said. “You prevent it from happening or you don’t.”

Eileen Sullivan, Shaila Dewan and J. David Goodman contributed report.