Daley said many people and parents called Duncan, not just politicians.
The Chicago Tribune reports aldermen, state lawmakers, and others appealed to Duncan's office on behalf of students who weren't admitted to coveted schools.
The mayor appointed Duncan as the public schools' chief executive officer, and he says Duncan acted properly.
"If someone complained: 'My child did not get in the school, What can I do?' He sent in to the principal to review, which is the right thing to do. There's no favoritism, as Arnie pointed out. He just sent everything-- any complaint they had-- he sent it right to the school," said Mayor Daley.
Duncan headed the public schools from 2001 until he joined President Obama's cabinet.
Federal investigators are looking into admissions practices at the city's top high schools.