School shootings like the recent one in Santa Clarita, Calif., have focused the nation's attention on school safety. And schools across the U.S. are wrestling with how to prevent themselves from becoming the site of the next tragedy.

Many schools are turning to highly visible "hardened" security measures. For example, at least eight states now have laws mandating active shooter drills in schools. But there's little research yet that shows that those drills are effective. Meanwhile, a new comprehensive report from the U.S. Secret Service underlines the agency's previous findings that there is one safety approach that does work: threat assessment, as part of a comprehensive program of social and emotional support for students.

Active shooter drills can scare vulnerable children

A new law in Illinois requires students to participate in active shooter drills at school. The drills often involve students hiding in the classroom and sometimes evacuating the school. Some parents welcome the preparation.

"I don't see any way that the drill can do more harm than if your child was caught up in a real situation and did not know what to do," says Ronick Frazier, who has two daughters in Champaign, Ill., schools.

Another Champaign parent, Dianne, says she has seen the harm these drills can do. Her daughter Rory, 7, is on the autism spectrum and has attention deficit hyperactivity disorder. (We aren't using Dianne's full name to protect her daughter's privacy.)

In the spring, Rory's school had a "hard lockdown drill" in which students were told to stay in their classroom, remain silent and keep calm. Dianne says Rory came home upset and worried about bad guys with guns.

"It was heartbreaking. She was screaming and yelling. She loves school, and she kept yelling, 'I don't want to go back. I don't want to go back.' " After seeing Rory's reaction, Dianne says she doesn't think any kids should have to participate in drills like these.

"Fair enough," says Melissa Brymer of the National Center for Child Traumatic Stress. "But an emergency can happen at any point in a school day."

Brymer believes these drills can save lives, but as one recent study from Ball State University found, there's little evidence to prove that.

The study says that's partly because these incidents are so rare that there aren't enough examples for social scientists to find reliable patterns in.

Child psychiatrist Steven Schlozman says researchers have collected anecdotal evidence showing that these drills can be challenging for kids with anxiety and developmental disorders, like Rory.

"Despite people being supercareful to make this a more palatable exercise for them, they still get pretty, you know, at best unnerved and at worst pretty traumatized," Schlozman says.

Schools with lockdowns still have shootings

Meanwhile, the recent Secret Service report has shed new light on security measures such as active shooter drills.

The investigators combed databases for as many incidents as they could find in which a current or recently former student brought a weapon to a K-12 school and harmed someone. They excluded drug- or gang-related incidents. They identified 41 targeted school attacks from 2008 to 2017.

According to the report, 83% of the attacks were over in five minutes or less. And 68% of the schools already had a lockdown procedure in place — making it the most common security measure among schools in the report. Of course, that doesn't necessarily mean a lockdown didn't limit the scope of an attack.

It's also worth noting, since much of the concern over lockdown drills looks at their impact on the youngest children, that only one of the targeted attacks in the report took place at an elementary school.

The report's lead author, Lina Alathari, says rather than focusing solely on what happens after an attack begins, schools need a much more comprehensive approach, emphasizing "multidisciplinary" prevention in the years, months and days before a student actually shows up at school with a weapon. That means bringing together teachers, administrators and mental health professionals, along with law enforcement if needed.

That may be surprising coming from an agency known for its metal detector sweeps and guys with the earpieces. But Alathari says the bulk of what the Secret Service does involves prevention and threat assessment.

She defines threat assessment as a proactive approach in which schools "identify students who are doing concerning behavior or may be in distress and getting them the help they need before they even resort to violence as an option."

One common source of distress, according to the report, is bullying and ostracism. Four out of five of these attackers were bullied at school, and in most cases the bullying was severe and took place over a long time period. Attackers were much more likely to be victims than perpetrators of bullying, although that was fairly common as well.

In the aftermath of the Columbine attack in 1999, in which two Colorado students killed 13 people at their high school and injured more than 20 others before taking their own lives, the Secret Service published its first review of similar incidents. Back then, 71% of attackers had been bullied. Since then, Alathari says, "it's interesting": Despite two decades of anti-bullying legislation, anti-bullying assemblies and anti-bullying curricula in schools, today the incidence is even higher.

"Assess the climate of your school," she says to school leaders. "What is the perception of bullying? What kind of intervention is taking place?"

Alathari says there is some evidence that a better school climate can directly save lives.

Alathari found that 9 out of 10 attackers give a warning sign in the form of concerning or threatening statements. The report includes anecdotes of such warnings, including this one:

[He] tweeted, "It won't last...It'll never last" and texted his ex-girlfriend asking her to meet after school so he could say goodbye. He also sent her a Facebook message that said, "read my messages tomorrow from 7:15 to 12:30." The attacker posted on Instagram, "Tell my mom I love her," and included an emoji image of a gun."

Those messages came from a 15-year-old student who fatally shot four of his classmates and injured one other in his high school cafeteria, before killing himself.

But why don't people report these warning signs? Over a decade ago, the Secret Service conducted a small study in which it talked to "bystanders" — students who had heard warnings from a fellow student before a planned attack. In six cases a shooting was prevented, and in a further nine cases a shooting happened.

In the bystander report, students who came forward told investigators they did so because they had a strong relationship with at least one adult at the school and they thought their concerns would be taken seriously. Students who did not come forward said that they thought the school would not take appropriate steps or they would get in trouble themselves.

Like the Ball State study, Alathari emphasizes that targeted attacks of this kind are extremely rare. The new report excluded attacks that seemed to be related to drugs, gang violence or disputes that merely spilled over onto school property. They were left with an average of four shootings or stabbings per year across hundreds of thousands of schools, and the report found no upward trend in the frequency or severity of attacks over time. That's yet another reason, she says, to focus on prevention efforts that can improve the school climate overall — whether or not the worst-case scenario happens one day.