Cosby, 69, who holds a doctorate in education, was the keynote speaker Wednesday at the Power of Parents Conference, which was arranged by the Chicago Public Schools.
Continuing themes that sparked controversy two years ago, Cosby -- revered as Dr. Cliff Huxtable on "The Cosby Show" -- told the parents in a hourlong speech, "I hate to tell you what you're doing wrong."
He said many African-American parents had lost a sense of responsibility that had preserved previous generations of black Americans regardless of their low economic status, the Chicago Sun-Times said.
"We have lost some things," Cosby said, "and I can't believe one of them is how to parent."
Cosby made headlines in 2004 when he publicly scolded minority parents for losing control of their children, resulting in teenage pregnancy, school dropouts and incarceration.
He later spoke to more than 9,000 teenage boys and fathers on changing to a more positive behavior.