They had more than half a dozen San Francisco agencies trying to get on the same page when it comes to something like this, should it happen for real.
They even have agencies in Oakland observing to see how this works. This is the first such drill in San Francisco, but organizers say it won't be the last.
It is a drill and it looks that way. There is no one running, people are extremely calm, even the victims.
"At this point in time we have a suspect in custody and another suspect we believe is barricaded in another part of the school," said Sgt. Neville Gittens from the San Francisco Police Department.
It's a drill, just a drill, but important enough to have San Francisco police, fire, sheriff's office, Emergency Medical Services, the San Francisco School District, traffic and public works, the drill at Saint Ignatius High School is a time to learn.
An incident command system has been put in place; different supervisors for different areas.
"They'll have made medical group supervisors who will coordinate all of the triage, the treatment, the transport of the victim," said Lt. Mindy Talmadge from San Francisco Fire Department.
And when it's all over, and the wounded and the dead have been sent back to class, city agency representatives will go to school themselves.
"At the end of this exercise, there will be a debriefing among all of the agencies, and the personnel in the school. So it's a good exercise to prepare us if something like this were to happen," said Sgt. Gittens.
Some students were evacuated from the school, and what the learned here will be used for the next drill or if it becomes real.