Monday, Denver Public Schools Chief Safety and Security officer Michael Eaton showed 9NEWS the district's dispatch center, where they are in constant contact with Denver police.

From the dispatch center security officers monitor over 2,000 cameras throughout the district around the clock.

"We are looking at installing access card readers in several, if not all, schools in the district. Cards which will give us the ability to better secure our schools," Eaton said.

Eaton says all the teachers have been trained on how to do lockdowns. Each school is required to do two lockdown drills a year.