A high school in the far northwest suburbs of Chicago was locked down for about 20 minutes on Wednesday afternoon after the sound of two gunshots rang through the halls.

But the shooting -- done with blanks -- was all part of a drill to educate students and staffers at Cary-Grove High School in Cary, Ill., on what to do in the event of a real emergency. Cary is located about 45 miles northwest from downtown Chicago.

"For fires through fire drills, we prepare them for tornadoes through tornado drills and unfortunately a reality of today is that we also need to prepare them for other safety concerns that are more immediate," said district 155 spokesman Jeff Puma.

Police and administrators did a complete sweep of the building after two shots were fired at opposite ends of the school. Students were ushered to the corners of their classrooms as if a gunman were roaming school grounds.

Reaction from students was mixed.

"We learned, like, where to go and stuff, so that was helpful," said one student.

"I feel like they could have done it better. Honestly, more blanks around the school because for the most part you really couldn't hear it," said another.

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Despite the difference of opinions, administrators and police said the information learned could be life-saving.

"The idea was to allow our students to have something in their head of what it might sound like in order to react more quickly," said Puma.

Many parents notified of the "code red simulation" earlier this week said the simulated gunfire was too strong a tactic.

"It's sad, but the reality is these things happen," said Cary police Chief Steven Casstevens.

A district official said Wednesday's drill wasn't the first conducted in the wake of the Sandy Hook school shooting. The first was done just four days after the Newtown, Conn., tragedy.

Previous story from NBCChicago.com: Parents uneasy about simulated school shooting