Last fall, Mayor Rahm Emanuel persuaded teachers at 13 elementary schools to waive provisions of their union contract in order to add 90 minutes to their day. In exchange, teachers received $750 stipends and each school got up to $150,000.
The union says the new deal guarantees that teachers will be properly compensated for the extra time they've worked this school year, above the stipend.
Teachers' union president Karen Lewis calls the agreement "a great victory for collective bargaining in Chicago."
All CPS schools will go to a longer school day beginning this fall.
"We choose to focus on the classroom, not the courtroom and this settlement is an attempt to avoid the courtroom," said CPS' Becky Carroll, chief communications officer. "Moving to a full day will provide additional instructional time students need with teachers learning critical subjects like math, reading and science so they are better prepared for success in college and career."
The Associated Press contributed to this report.