After the Columbine shooting, the mindset on school campuses changed from one of waiting for a SWAT team to arrive to form a plan and enter the building, to having the first officers on the scene, who immediately find and stop the shooter in order to save lives.
Officers said the most important aspect for any school or business is to have a plan in place and practice it frequently to minimize panic and maximize the number of lives saved.
"It boils down to action beats reaction," Sgt. Brian Hill said. "You've got a very determined person who has planned this out, and probably put into their mind they're going to die from a self-inflicted gunshot wound at the end."
Police said you can't predict when a shooter will strike and can't stop it from happening, so being prepared is the best chance to react quickly when it does happen.
Even having armed officers at schools can't stop the tragedy, because campuses are large and these incidents can happen in a matter of seconds.
"A very determined person can do a lot of damage in a hurry," Sgt. Luke Sherman said.
In fact, it could be all over before officers even arrive, so what then?
The Department of Homeland Security funded a video that tells people what to do.
First, run. If you can get out, take as many people with you as possible.
If you can't escape safely -- hide. Get behind a locked door or something heavy that would give you protection from gunfire and keep quiet.
If you can't run or hide, your last alternative is to fight and do whatever you can to survive.
That may work with grownups, but children are dependent on the plans and actions of their teachers and administrators.
One area school's plan is to have teachers and students get into their classrooms and lock the doors.
Other schools are looking at electronically locking down other buildings as soon as a threat is identified.
Still, police say giving children information could make their reaction time faster and increase their chances of survival.
"Be vigilant and talk to your kids about this. Certainly no mother or father wants to talk to their 6- or 7-year-old but it's the reality of our world," Hill said.