Schools are now treating mass shootings like tornadoes and earthquakes — disasters beyond their control that students must be prepared for at all costs.

A new survey from the Education Department found that 70 percent of schools practice school shooting drills, up from 53 percent in 2008. They're most common at suburban schools, although they're generally widespread: 75 percent of suburban schools held a shooting drill in 2013.

They might be doing more harm than good. American schools are safer than they've ever been. If the worst happens — someone shows up at a school intending to kill dozens of students — there's no evidence that having conducted mass shooting drills actually helps.

Meanwhile, school employees and parents are beginning to complain that the drills themselves can be traumatizing.

Great news: going to school is very, very safe

School shootings seem scarily common. In the two years after the Sandy Hook elementary school shooting in December 2012, there were 49 shootings at K-12 schools in the US, according to a report from Everytown for Gun Safety, a gun control group; 15 of those shootings killed at least one person.

News coverage gives the impression that schools have become more violent, not less, since the Columbine mass shooting in 1999. But federal data shows the number of students killed at school has actually dropped since the 1990s, even as public school enrollments climbed:

The risk of a child getting killed by someone else at school in 2011, the last year for which there's final data, was about 1 in 5 million. That's slightly less likely than being struck by lightning. (In 2012, Sandy Hook drove up the homicide rate, but it doesn't seem to have changed the overall trend, according to the Education Department. The Everytown study appears to back this up.)

It's possible that new safety measures after Columbine, including drills, contributed to the quick drop in the murder rate. But it's more likely that it's part of a bigger trend of declining crime and violence at school. The rate of "serious violent victimization" among students — rape, sexual assault, robbery, or aggravated assault — was about 1 in 1,000 in 2011, down from 1 in 100 in 1995. In 1995, 10 percent of students were victims of some kind of crime at school; in 2011, just 4 percent were.

There's no evidence that mass shooting drills work

Since Newtown, an industry has sprung up to assuage schools' and parents' fears: bulletproof whiteboards and classroom door barricades. An Alabama middle school principal asked students to bring in canned food so that they'd have a weapon if an armed intruder broke into their classroom.

In 2003, less than half of schools drilled students on what to do in case of a mass shooting; now 70 percent do. Shooting drills are nearly as common as drills for natural disasters, which are in place at 83 percent of schools.

The drills themselves have gotten more elaborate. Some schools simply close and lock the door, turn out the lights, and ask students to stay quiet until the all-clear. But others, increasingly, are turning their hallways into an imitation of a real mass shooting, complete with police officers firing BB guns and drama students enlisted to play victims, made up with fake blood and bullet holes. Occasionally, the drills are sprung on teachers and students without warning.

A substantial amount of time, money, and energy is being spent preparing kids to deal with a threat they'll almost certainly never have to face.

Preparing for something unlikely is the point of disaster preparedness. Most schools don't burn down or get hit by tornadoes, either, but parents accept fire and tornado drills anyway. The difference is that sheltering in the basement in a tornado or evacuating a burning building in a fire are proven strategies. They don't always succeed, but they're the best guidance available.

Mass shootings, on the other hand, are as unpredictable as they are unlikely. There's no clear evidence that the more dramatic drills help; in fact, there isn't even consensus on what students should be practicing. Students and teachers used to be taught to lock the door, stay away from windows, and wait for help to arrive. Now more than 1,600 schools have been trained on the ALICE method, which suggests fighting back against the shooters instead.

Teachers have complained that they've been physically hurt or emotionally traumatized by the ALICE drills, the Wall Street Journal reported in September. National groups of psychologists and school police say the more active, theatrical drills should never be required for all students, and that they can be disturbing for students who have experienced violence in the past.

And nobody knows if any of this will really work in the event of an active shooter. Schools now go into lockdown all the time, usually for threats much more removed than a gunman in the hallway — a nearby bank robbery, or a domestic dispute between two parents. Lockdown drills seem to reliably produce more lockdowns. It's not clear if they really make schools safer.