Schools across the country are now taking their own precautions to be prepared for the unthinkable.
In the wake of the tragic mass shooting at a Florida high school, would you know what to do in a similar situation?
Inside Edition went to one New Jersey high school as they prepare for an unthinkable nightmare they pray will never happen.
It's called a "Code Red," an active shooter alert in the building that results in a lockdown.
It's intended to be as realistic as possible with cops and students covered in fake blood. The drill even included a car bomb.
The Department of Homeland Security is sponsoring drills just like it across the country to test the response of police and school authorities.
In California, the Los Angeles County Sheriff’s Department produced a video that teaches survival techniques for anyone caught in an active shooter situation.
Among them is to barricade the door with any large items in the room like desks, cabinets and boxes.
They also advise turning off the lights and silencing your cell phones.
As a last resort, improvise a weapon — anything that can disrupt the shooter's ability to see, breathe or control their firearm — like a fire extinguisher.
At a parochial school in New Mexico, many of the teachers carry guns as a precaution.
One pastor carries a .45 in a case that looks like a Bible. The principal is also armed with a .38 semi-automatic pistol.
In one of their classrooms, students say they feel safer knowing there are adults with the weapons.
Safety and security expert Bill Stanton suggests that trained dogs be assigned to schools to assist in taking down a shooter.
Stanton says that fear will often keep a shooter from firing on the canine.
“The first thing you think of is fear," Stanton said. "That is all you need to buy that time to get those kids in a safe space or to evacuate completely."
An organization called K9s4Kids helps place K-9 dogs with officers who patrol schools.
Psychiatrist Jonathan Sherin, the director of the LA County Department of Mental Health, says many schools now have "threat assessment teams" that identify suspects before they strike.
“Comments in class, comments to other students, erratic behavior, isolation — these are all signs that are potentially concerning," he told Inside Edition.