After this week's deadly shooting in Northern California, a lockdown is being credited for saving the lives of students and teachers.
So what exactly happens inside the classroom during a lockdown.
On Tuesday, the same day of the shooting, Rancho Bernardo High School held a lockdown drill.
In fact, schools in the Poway Unified School District will have up to eight emergency drills every year. They include fire, earthquake, evacuation and lockdown drills.
Once every semester, there is a lockdown drill.
In the San Diego Unified School District, they’ve added a second lockdown drill to its school year.
"We'll shut the door and turn off the lights and lock it," said Terri Rogelstad, a teacher at Rancho Bernardo High School.
The first priority is to move students away from windows. In Rogelstad’s classroom, there are two back rooms where students drop to the floor and are told to stay quiet. Window blinds are closed and computer screens and lights are turned off.
Teachers are instructed not to open the doors, even if the person identifies themselves as a law enforcement officer.
"Our staff is trained not to open the door no matter what anyone is saying. They know that if that was a real situation where there was a lockdown, there would be, the law enforcement would have the keys and would enter the door," said Bill Egan, the Assistant Principal at Rancho Bernardo High.
Egan is also the school’s emergency coordinator.
At Rancho Bernardo High, they know first-hand the importance of the drills. In May 2017, the school was on lockdown for almost two hours after threatening notes were found on campus.
"I think that this time around, the drills are a little bit more serious because they feel the weight of the real thing when we did have the lockdown," said Jalen Rasoul a student and ASB President at Rancho Bernardo High.
Meanwhile, Egan said the drills offer a constant learning experience. Among issues he will address is whether students are taking the drills seriously.
"When we see that happening we go then go back and address it with our students and teachers that 'Hey, this classroom, we could hear noises,'" said Egan.