Nearly 60 percent couldn't even read at the third-grade level when they were booked in.
At the largest of the three facilities, the Illinois Youth Center St. Charles, all but nine of the 72 youths had dropped out of school entirely by the time they were incarcerated.
These figures, calculated by the Tribune from newly obtained state prison data, serve as a grim reminder that absence from school in the early grades is often the first warning of criminal misconduct that can destroy young lives as well as burden society with the costs of street violence, welfare and prison.
The records underscore the stark consequences of a crisis in K-8 grade truancy and absenteeism in Chicago that officials long ignored but have promised to address in the wake of a Tribune investigation that found tens of thousands of city elementary students miss a month or more of school in a year.
The prison data consist of raw numbers, but behind them is a ragged parade of youths whose cases fill the docket in Cook County Juvenile Court.