After Parkland, there have been many calls to make schools a "harder target" — for example, by arming teachers. But there's a decent amount of research out there on what actually makes schools safer, and most of it doesn't point to more guns.

On the Friday after the deadly shootings at Marjory Stoneman Douglas High School in Florida, Matthew Mayer, a professor at the Rutgers Graduate School of Education, got an email during a faculty meeting.

The email was from Shane Jimerson, a professor at the University of California, Santa Barbara. Both specialize in the study of school violence.

That email led to nearly two weeks of long days, Mayer says, for some of the leading experts in the field. On conference calls and in Google docs they shaped a concise, eight-point "Call for Action To Prevent Gun Violence In The United States of America."

About 200 universities, national education and mental health groups, school districts, and more than 2,300 individual experts have signed on to support this document in the weeks since.

Their topline message: Don't harden schools. Make them softer, by improving social and emotional health.

"If we're really talking about prevention, my perspective is that we should go for the public health approach," says Ron Avi Astor at the University of Southern California, who also helped draft the plan.

A public health approach to disease means, instead of waiting for people to be rushed to emergency rooms with heart attacks or the flu, you go into the community: with vaccinations, screenings, fruits and vegetables, walking trails and exercise coaches. You screen and regulate environmental hazards, like a nearby polluting factory. You keep watch on reported cases of illness, to stop a new outbreak in its tracks.

A public health approach to school shootings, Astor explains, would be much along the same lines.

Instead of waiting for people to, again, be rushed into emergency rooms, you go into the community with preventive resources. You do your best to lower the background levels of bullying and discrimination. You track the data and perform what is called "threat assessments" on potential risks.

And, these experts say, you remove the major "environmental hazard" that contributes to gun violence: the guns. The eight-point plan calls for universal background checks, a ban on assault-style weapons, and something called Gun Violence Protection Orders: a type of emergency order that would allow police to seize a gun when there is an imminent threat.

What sets this call to action apart from other policy proposals is not gun control, however, but the research-based approach to violence prevention and response. This is a long haul, say the experts, not a quick fix.

"No matter what you try to do by just hardening the target, we've learned that having the armed officers isn't necessarily going to stop it," says Matthew Mayer at Rutgers. "Having the metal detector or the locked doors isn't going to stop it. The hard work is a lot more effort. You'd better start thinking in a more comprehensive manner about prevention instead of reacting."

Prevention: The first step

School climate may sound fuzzy or abstract. It means the quality of relationships among the students and the adults in a school. It's affected by the school's approach to discipline and behavior, the availability of professionals like counselors and social workers, as well as any social-emotional curriculum taught in the classroom.

School climate, in turn, affects students' mental and emotional health and academic success. And research by Astor and others has consistently found key factors that can make schools safer: cultivate social and emotional health, connect to community resources and respond, particularly, to troubled students.

Why does this matter? Well, for one thing, the very kids who bring weapons to school are more likely to report being bullied or threatened themselves. They may be fearful of gang violence and feel a need to protect themselves on the way back and forth to school.

Or, they may be individually ostracized and aggrieved. This is true not just in the United States, says Astor, but in "Kosovo, Canada, Chile, Israel, the kids who bring weapons to school are reporting tons of victimization."

So, if you devote resources to shutting down bullying, discrimination and harassment, there is a chance to de-escalate conflict before it starts.

And research shows that school climate measures really work. In fact, there has been a steady downward trend in bullying and harassment over the past decade, which Catherine Bradshaw at the University of Virginia attributes in part to evidence-based social and emotional measures.

The witnesses

There is a second reason a better school climate can cut down on violence. It's what Astor refers to as the role of the witness.

He again cites the example of California, which does a comprehensive annual survey. There, 20 to 30 percent of students above the elementary level consistently report seeing a weapon of some kind at school at least once during the year. That's conservatively more than half a million students, just in that one state.

Moreover, based on the survey, at least 125,000 of these students in California were actually threatened or injured by a weapon on school grounds. This includes things like knives and nunchuks as well as guns.

But what happens next?

If that witness, or that victim, has a strong relationship with an adult, they are more likely to report being menaced by a weapon. Whereas, if there is what Astor calls a "no snitching culture" in the school, or the witness fears for their safety, nothing will be done.

He says he's not urging schools to punish or expel the kid who brought the weapon, but, instead, to use "education as an intervention."

This approach is applicable not only for mass shootings, he says, but for violence that arises from disputes between students or when gang violence in the community spills onto school grounds.

And, he says preventing gun violence also means looking at suicide. Suicide is just behind homicide as a leading cause of death for teenagers. When a weapon comes to school, self-harm may be the plan, and a school-climate approach addresses that threat as well.

The researchers' policy plan calls for assessing school climate nationwide; reducing "exclusionary practices" like suspension and expulsion; maintaining physically and emotionally safe schools; and staffing up with specialists like counselors, psychiatrists, psychologists and social workers, both in the school and in the community.

Emergency mode

While school climate is an ongoing background effort, the public health approach has an emergency mode when it comes to violence. It kicks in when someone does report a person bringing a weapon to school or talking about violence. It's called a "threat assessment."

After the Columbine shooting in 1999, the FBI and the Secret Service each conducted studies of school shootings and shared their knowledge with the nation's educators. They found that there was no one "profile" of a school shooter. But, almost all students who committed homicide had told someone of their intentions.

So, the two law enforcement agencies recommended that schools copy what the Secret Service does when someone makes a threat on a government official. Threat assessment has been required by law in Virginia's schools since 2013, and adopted in many other places.

A threat assessment team consists of the principal, school counselor, school psychologist and a school-based police officer. They talk to the people involved and any witnesses. They try to figure out if the threat is serious: Is it specific? Is there a detailed plan? Is there a weapon?

In a school, the next steps include notifying parents, taking steps to protect victims, and referrals to mental health and law enforcement if appropriate.

Threat assessments are not a fail-safe. A local ABC affiliate in Florida did report, based on school records, that a threat assessment was ordered for Parkland shooting suspect Nikolas Cruz, based on an incident that happened in January 2017, a year before the shooting.

But Dewey Cornell at the University of Virginia, another author of the Call to Action, says researchers have gathered good evidence to support the technique, when implemented fully as in Virginia. Among the positive impacts, he says, are "reduced suspensions and reduced bullying, students and teachers reporting that they feel safer, and students reporting a greater willingness to report threats of violence."

His research also shows that less than 1 percent of threats are ever carried out.

The researchers are hopeful that their Call to Action will break through the noise. But they've been here before, Mayer says. A group of his colleagues wrote something similar in 2012 after the shootings at Sandy Hook Elementary School, and after a group of school shootings in 2006. Mayer hopes, this time, people will be paying attention.

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