Police said they were called to Curie High School around 9:30 a.m. for a 15-year-old boy in possession of a gun.
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School officials said they were told one of the students had brought a gun to school and immediately contacted police.
The teen was taken into custody and charges are pending. No one was injured, school officials said.
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A letter was sent out to parents, saying in part, "I am committed to ensuring a safe and positive environment at school, and I know that situations like this can be concerning for our community."
The Chicago Public Schools Office of Safety and Security is also involved.