CHICAGO - Hundreds of Chicago students have been sexually assaulted over the past decade after the third largest public school system in the US failed to implement basic safeguards like conducting adequate background checks or reporting abuse to authorities.

Since 2011, Chicago Public Schools (CPS) investigators have discovered “credible evidence of misconduct” in 230 reports of sexual abuse involving adults and students, according to Chicago Tribune, which carried out a wide-ranging investigative report entitled “Betrayed.” But the newspaper estimated the actual figure could be much higher because the CPS did so little to understand and tackle the problem.

The school system employed “ineffective background checks,” the Tribune said, which failed to weed out employees with criminal convictions and arrests for sex crimes. More than 370,000 students are enrolled in CPS, which employs nearly 36,000 people.

CPS chief Janice Jackson responded to the report by promising a “top-to-bottom review” of the school system’s safety procedures, to be conducted by an independent lawyer.

“Like many parents this morning, I’m sick to my stomach,” Jackson said on Twitter. “And like many parents, when I send my children to school, my expectation is that they are safe from harm.”

A Tribune investigation identified 72 school employees who were alleged to have committed offenses over the past decade. They included school deans, teachers, coaches, counselors, security guards and others.

When students reported abuse, the results of internal probes were kept secret despite the state’s mandated reporter law, and students often did not get the proper care they needed to deal with trauma, according to the newspaper.

Even in cases where school employees acted swiftly, they subjected young victims to repeated interrogations, inflicting additional psychological pain on the survivors.

The Tribune cited the case of a teacher hired in 2009 despite a prior prowling charge and a “window peeping” conviction at the home of a little girl.

In another case, a high school security guard was allowed to keep for years his job despite multiple convictions linked to groping.

Jackson said the district will work to “ensure that our hiring practices, background checks, training, and handling of sexual assault and misconduct allegations are the best policies and practices to protect our students.”

Among the changes the district outlined were better screenings of athletic staff and periodic background checks for all employees.