In September, hundreds of CPS students received glossy postcards from the Noble Charter Network soliciting them to switch schools.
The postcards were directly addressed to students in sixth through eighth grade and included the students' home address and current school.
In a statement, the district said, "CPS is deeply troubled by any violation of students' privacy. Upon learning of the origin of this breach, CPS immediately shut down the employee's access to student data systems and began the process of notifying families whose directory information was breached. CPS also contacted the Inspector General and initiated a thorough review of security procedures."