The gun discharged accidentally on Tuesday, wounding the 15-year-old teen and another 14-year-old student in their legs, the Chicago Tribune reported.

The boy is charged with felony aggravated use of a weapon on school grounds, police said Wednesday.

Police are trying to find out how the boy got the 9mm Ruger pistol into the school.

He had the gun in his lap in the back of a classroom and was showing it to another student when it discharged, police said. The bullet traveled through his left thigh and then went through the right thigh of the other student, police said. Both teens are in stable condition.