It's not clear how the gun came to administrators' attention, but authorities said "there is no active shooter or active threat" on campus at about 11:30 a.m.
By about 11:50 a.m., the decision was made to evacuate the middle school, according to police. Fifth and sixth graders were taken to Riverside Elementary, 1400 Centre Ave., while seventh and eighth graders were brought to St. Margaret's at 235 Spring St., the department said.
Parents should pick up their children at those locations, police added.
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