By Nicole Chavez and Alaa Elassar, CNN

(CNN) -- School fire drills became popular decades ago after several deadly fires triggered changes in safety codes. Today, teachers and children are preparing for something entirely different: mass shootings.

A gunman tried to break into a remote Northern California elementary school on Tuesday but officials say, the quick action of school officials "saved countless lives and children."

The building went on lockdown, a teacher rushed to block a classroom's door with a computer and students ducked under their desks. Those responses have become the new normal as more schools are being forced to adapt to more elaborate safety measures.

Two thirds of schools in the US conduct active-shooter exercises and nearly all of them have a plan if a shooter comes into the school, the Government Accountability Office found in a recent survey of schools.

"I think everybody, no matter where you are, needs to think about this. If you're in a school, in a college, if you go to the movies we should all be thinking about what are we going to do if a crisis breaks out right here," said Christopher Combs, FBI special agent in charge, after last week's church massacre in Texas.

This year, there has been about one mass shooting every single day, according to the Gun Violence Archive, a non-profit that tracks gun-related violence in the US.

'You might lock down, you might try to escape'

Sara Rounds and her colleagues recently took part in a series of simulated active-shooter scenarios at their western Indiana school.

"When I did enter teaching, you know, this was not a thought in my head. But this is where we are now," Rounds, a first grade teacher at Jackson Township Elementary in Clay County, Indiana told CNN affiliate WTHI.

Through training programs like ALICE -- Alert, lockdown, inform, counter and evacuate -- Rounds and other teachers are learning how to barricade doors with desks and chairs, run away from gunfire and throw everything from pencils to staplers at a potential shooter.

"It's not really defense techniques, it's not martial arts of any kind. It basically just gives them options," Jeffrey Fritz, the Indiana school's superintendent told CNN affiliate WTHI.

"You might alert, you might lock down, you might try to escape, it just depends on the situation," he added.

But training teachers is just the first step. The school plans to teach students how to make choices during an active shooter situation.

"We are going to teach this to the kids in a very kind way, not using harsh words, kid friendly, so I think our kids will really grasp on to this," Rounds said. "This is nothing new here to society, it's in the news a lot. They understand what our world is going through unfortunately."

Don't freeze, have a plan

Those who plan for an active shooting situation are more likely to react quickly rather than freeze, said Katherine Schweit, a former senior FBI official and an active shooter expert.

"We're not talking about making a decision on what to make for dinner. We're making a decision on how to survive," she said.

During the Virginia Tech shooting in 2007 and the 9/11 attacks at the World Trade Center in New York, people delayed evacuations or denied the possible danger rather than respond, according to a 2013 report released by the Federal Emergency Management Agency.

"People freeze. And if you train yourself to work past freezing, past the moment of hesitation, you save your life. Or you save a life of another," Schweit added.

It is recommended that if possible, Schweit said, that victims caught in shootings run as fast and far as possible.

"I'm a total believer in run, run, run if you can (to) safety. Because you can't get killed if you're not there. But if you have to hide or fight, you have to be prepared to do that," she added.

Other security measures

Active shooter training is relatively new in some schools across the US. For years, schools have employed school safety officers, lockdown drills and implemented security systems that require visitors to sign-in and produce photo IDs.

After the Columbine shooting in 1999, schools installed metal detectors and shifted restrooms away from entryways. While just a few weeks ago, a private school in Florida began selling bulletproof panels for its students' backpacks.

Schools across the country have also created "threat-assessment teams" to prevent shootings by identifying behaviors like mental illness, drug abuse and disruptive conduct in students.

Initially, all Virginia public schools were required by law to create those task forces. But now, dozens of schools across the country have adopted the practice.

In 2002, Texas State University in San Marcos, Texas created the Advanced Law Enforcement Rapid Response Training (ALERRT) in partnership with several Central Texas law enforcement agencies to address the need for active shooter training.

Since its creation, more than 85,000 law enforcement officers have been trained through the program.