Schools CEO Jean-Claude Brizard said the longer days are part of an effort to improve student performance in core subjects.
The new schedule will include a longer day and the elimination of a 14 minute homeroom period.
Brizard discussed how schools might use the time.
"We're going to allow some innovation, but provide quite a bit of guidance, because we want to make sure that the reading and the writing and the math and the arts are included in this work," said Brizard.
The Chicago Teachers Union says extending the school day is a public safety issue because kids will be getting home later.
The union is also concerned about students having time for studying and after school jobs.