Students at 243 Chicago public schools began a seven-hour school day.
Parent Pamela Johnson took her children to school Monday ready for the longer day.
"I think it's a pretty good idea to have the kids to go longer because kids do need more attention in school," Johnson said.
Until now, the district had one of the shortest school days in the country.
Chicago Mayor Rahm Emanuel welcomed students, teachers and staff back to Beidler Elementary school in the city's East Garfield Park neighborhood, where grade school students will move to the seven-hour day.
"For far too long we as a city have denied our teachers and our children the kind of day they need and they kind of year they need ... the future they deserve," said Emanuel.
CEO of Chicago Public Schools (CPS) Jean-Claude Brizard rang the bell Monday to signal the start of classes at Robert Lindblom High School in the Englewood neighborhood.
Under the new standard, high schools will have a 7.5-hour day with more science, writing and college prep.
The changes are talking place as a possible teachers strike threatens the school year. Last week, Chicago Teachers Union (CTU) President Karen Lewis called on the rank and file to prepare for a strike, increasing the pressure on the ongoing negotiations with CPS.
"I'm praying that they're still going to compromise, that a compromise is still going to come out of this," 27th Ward Ald. Walter Burnett said.
Negotiations between CPS and the CTU continue.
For 8-year-old Cormarion Lofton, the first day of school was just about being a third grader.
"I''m extra excited, and I like school to be extra fun," he said.
If the teachers unions does decide to strike, teachers would have to give 10 days' notice before walking the picket lines. Many eyes will be on the negotiation process this week.