"We can't say it's a result of a problem with 'safe passage,' but we know it's not supposed to happen," Chicago Alderman Ariel Reboyras said.
A vicious attack on a 15-year-old girl has Chicago officials re-examining the city's "safe passage" system.
The program is meant to protect students on their way to school and back, with trained workers patrolling designated routes throughout the city.
But Tuesday's incident, which occurred 30 minutes before the start of "Safe Passage" patrol has raised doubts over the effectiveness of the program.
CNN's George Howell reports.