The alleged robbery occurred about 2:40 p.m. Friday at Palmer Elementary School, the Chicago Tribune reported.
Police said the 12-year-old put the replica gun to the alleged victim's chest and told him to "give me your money."
"When school officials learned of the incident, police were called and the [Chicago Public Schools] does not tolerate the presence of any weapon of any kind on school property for the safety and security of our schools, students, staff and visitors," a spokesman said in a statement. "School officials took the appropriate steps of notifying [the Chicago Police Department], who then took immediate action at the school."
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