(CBS) – Classes will resume Friday at Skokie’s McCracken Middle School, now that police have investigated a threat that had been posted online.

District 73.5 Superintendent Kate Donegan made the announcement in a “robocall” to parents Thursday evening. The decision to resume classes was made after consulting with police, she said.

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The school sat empty Thursday for a second day after anonymous users accessed students’ Instagram accounts and made some sort of threat against the school.

“The threat was deemed not credible,” Skokie police said in a posting on Facebook. “All persons identified and involved in this matter were juveniles.”

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Parent Laura Montgomery says the school made the right call in being cautious.

She says it’s a sad day when schools close over such incidents, but also an opportunity.

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“This is a wake-up call to all parents to be vigilant about knowing what’s going on with kids online and talk with them,” she said.