Students at thousands of schools across the United States walked out of class Wednesday morning to pressure Congress and state lawmakers to pass gun control laws.

More than 2,500 students had planned to join the National School Walkout out at 10 am in every time zone, according to organizers. They want Congress to expanding background checks to all gun buyers and banning assault-style weapons, such as the AR-15 used in the Feb. 14 shooting that killed 17 high school students in Parkland, Florida.

But so far, the Republican Congress has shown little interest in enacting such provisions. Instead, GOP lawmakers have been more focused on beefing up security at public schools and giving more money for safety training, including mass shooting drills.

On Wednesday afternoon, the House of Representatives is scheduled to vote on the STOP School Violence Act, a bill that doesn’t address guns but provides an annual $50 million grant to schools for training programs and upgraded reporting systems.

The bill would allow schools to use the money for mass shooting drills, which have become common in public schools since the Columbine school massacre. Since the Parkland shooting, a few states have also taken steps to beef up school security. Lawmakers in New York are considering a bill that would require all school emergency drills to include mass shooting scenarios. South Carolina lawmakers are considering a bill to require schools to carry out active-shooter drills every single month. Last week, Florida passed a school safety law that requires schools to conduct mass shooting drills twice a year.

The sad truth is that most public schools in the United States already do some sort of mass shooting drill. Nine out of ten public schools now drill students and teachers to respond to mass shootings, according to the National Center for Education Statistics.

These mass shooting drills have become the new normal, and a generation of American students have learned to lock and barricade their classroom doors the same way they learn to drop and roll in case of a fire.

Safety training companies, such as the ALICE Institute, regularly stage fake shootings as part of their training programs for schools. Here is how they teach elementary-school children to respond to a “bad guy” who bursts into class:

These sessions are a stark reminder of how American schools have changed since the 1999 Columbine school shooting. School administrators and state lawmakers have realized that a mass shooting can happen in any community, in any school, at any time, and that they need to be prepared if it happens.

School shooting drills became the new normal after Columbine

Since Columbine, 32 states have passed laws requiring schools to conduct lockdown drills or some form of emergency drill to keep students safe from intruders. Some states went even further after 20 children died in Newtown, Connecticut, in 2012. Now, six states require specific "active shooter" drills each year. That means the training must be specifically tailored to respond to an armed gunman out to kill. There is no consensus on what these drills should look like, but several states, including Missouri, require shooting simulations with police officers.

In the 2003-04 school year, when the National Center for Education Statistics began collecting this data, 46.5 percent of all public schools had conducted active shooter drills with students. By 2013-14, a year after Sandy Hook, that figure had climbed to 70.3 percent. In the most recent data, for 2015-16, “lockdown drills” — a broader category that NCES used for that year’s survey — were being conducted in 94.6 percent of schools.

"We are working in schools every day with innocent children who see school as a safe place," Henderson Lewis, Jr., the superintendent of the Orleans Parish School Board in Louisiana, told Vox. "We must do everything we can to prepare our kids for an unfortunate scenario."

New Orleans schools have been practicing lockdown drills for years, Lewis said, but they need to do much more. He is finalizing a plan to have school safety officers participate in mass shooting drills with police in empty school buildings.

The types of shooting drills vary by state and sometimes by school district. But here's what this data really means: Each year, nearly every student at an American public school is trained to cower under a desk or run for their lives to avoid being murdered by a gunman.

The limits of lockdown drills

The mass shooting at Marjory Stoneman Douglas High School in Broward County, Florida, has brought renewed attention to gun violence in schools.

Nikolas Cruz, a troubled 19-year-old former student, has been charged with 17 counts of first-degree murder for allegedly opening fire with an AR-15 on students minutes before the final bell rang.

As the shooting was taking place, tweets and video circulating on social media from inside the school showed students under lockdown, barricaded in classrooms, and hiding from the gunman.

The Broward County school district has been holding annual lockdown drills at its schools for more than 10 years.

There are basically two types of scenarios they train for. The first is the Code Yellow lockdown. This means teachers must lock doors and can continue teaching but cannot unlock the door until an "all clear" announcement has been broadcast over the intercom five times. When I worked as a crime reporter in Broward County, it was normal for a school to go into a Code Yellow lockdown when police were searching for an armed suspect in the surrounding neighborhoods.

A Code Red lockdown is for a situation like the one that happened in Parkland — where a gunman or intruder is on school grounds. In this scenario, teachers must lock doors, turn off lights, and move students away from windows. No one is allowed to talk or leave the room until the all clear is given. In both lockdown scenarios, teachers and students must ignore all other fire alarms or bells.

Yet a traditional lockdown drill doesn't teach students what to do when they come face to face to with a gunman, and that has led to some new approaches.

Drills that teach kids to run or fight back are becoming more common

After the Sandy Hook massacre, federal law enforcement agencies decided to take a closer look at effective ways to respond to school attacks. In one study of 84 mass shootings between 2000 and 2010, about a third (34 percent) involved schools. The FBI analyzed research on mass shootings and school violence and came up with common warning signs that a person might be at risk of undertaking a deadly attack:

The person experiences a significant personal loss in the weeks or months leading up to the attack, such as a death, breakup, divorce, or job loss.

The person recently begins collecting or buying multiple weapons; begins or increases target practice and weapons training; or develops a new and "contextually inappropriate" interest in explosives and fascination with previous shootings or mass attacks.

Few offenders had previous arrests for violent crimes.

The FBI's 2013 report, published with the Federal Emergency Management Agency, also urged schools to consider that typical lockdown drills may not enough. They suggested running off school property if possible, or hiding in a locked room if necessary, but even went so far to suggest fighting "the shooter to survive and protect others from harm."

That was a new idea for schools, and many districts began to take their advice seriously.

The Ohio-based ALICE Training Institute, referenced in the video above, is one of the companies that drills school police officers, teachers, and staff to do more than just hide. They teach students to barricade their classroom doors, run, scream, and throw things at a gunman.

About 4,200 school districts and 3,500 police departments have ALICE-trained personnel, according to the company's website.

These companies even provide the option of staging elaborate shooting drills, complete with fake blood and masked men with plastic guns (in one instance, involving a different company, a traumatized teacher in Oregon sued the school district for not making clear that it was just a drill).

Shortly after the Newtown massacre, a task force created by the Ohio attorney general's office released a report encouraging school staff to be more aggressive:

If an intruder enters and begins shooting, any and all actions to stop the shooter are justified. This includes moving about the room to lessen accuracy, throwing items (books, computers, phones, book bags) to create confusion, exiting out windows, and confronting (assault, subdue, choke) to stop the intruder. Tell students to get out anyway possible and move to another location.

Not everyone has embraced these tactics. There has been concern among school psychologists about the potential negative impact on children who participate in staged shootings. In 2014, the National Association of School Psychologists issued guidelines asserting that lockdown-based drills are ideal, as research shows they can be effective in minimizing injuries. Not much research has been devoted to the "run, hide, fight" approach, they cautioned, and schools should not make active shooter drills mandatory:

While one of the primary goals of crisis preparedness is to develop a sense of empowerment and control, armed assailant drills not conducted appropriately may cause physical and psychological harm to students, staff, and the overall learning environment.

This trend is super depressing

All the different views about the best way to train students to respond to mass shootings overlook the sheer insanity that such a conversation is even happening. It's depressing that the normal policy response to these tragic events has been to stage mass shooting drills at public schools, instead of developing policies focused on making the world less violent.

"We are going through tough times," said Lewis, the schools superintendent in Louisiana. "The world is changing."