The drill involved a familiar scenario - a gunman opens fire in a school.
A simulated drill - a shooter got inside Abbott Middle School - and opened fire. The drill involved more than 100 emergency responders using very real tactics:
The school and area was on lockdown. Officers and members of the SWAT team searched classroom by classroom, securing the building, rescuing students and trying to locate the mock shooter. It takes a lot of practice and teamwork.
"We're thinking about the worst kind of things that can happen and working together to try and make sure we are highly responsive," said John Heiderscheidt, coordinator of school safety and security.
And for the first time, the fire department was put to work inside, close to the danger zone.
"We actually put bulletproof vests on our medics; we've never done that in the past. It's a concept we are realizing we have to engage in because of society and the way it is," said Chief John Fahy, Elgin Fire Department.
In the end, everyone worked together. Ten students were mock-injured, and the suspect was stopped.
"We hope it never happens, but should it happen, we know that we've worked through with the school district, we've worked through with the fire department closely, and we know how each other will operate," said Deputy Chief Bill Wolf, Elgin Police Department.