HOMEWOOD, Ill. (CBS) — At a school in the south suburbs, police prepared for a terrifying possibility. CBS 2’s Jim Williams reports, fortunately it was all just a drill.

It began realistically enough with a call on the radio. Minutes later, squad cars arrived at the James Hart Middle School in Homewood.

“You can’t be too prepared today,” said Homewood Mayor Rich Hofeld.

Prepared for life in 2013 after so many school shootings.

The drill they staged had to seem authentic, so two armed intruders fired inside hallways and classrooms.

Even a mock scenario might have been terrifying for middle school children, so they were not here today.

“They’re absolutely too young,” said Shelly Marks of the Homewood School District.

Instead, students from Homewood-Flossmore High School volunteered, like senior football player Cashell Brown.

“It was scary at first because I was just sitting down. I saw a police officer with a gun running,” said Brown.

Actually, many police officers stormed the school, very cautious in a place normally walked by 10 year olds.

The drill could not have been more grim. The most welcome words this morning “You can all get up now.”

First responders from several south suburbs took part,learning to communicate with one another. According to law enforcement officials, here’s what has changed since the Columbine High School massacre 14 years ago: police officers will now storm a school while the crime is in progress, they will not wait.

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