CHICAGO (CBS) — After days in the deep freeze – schools across the Chicago area have been warmed up and prepared to welcome back students on Wednesday.

Sorry kids, winter break is over. It’s back to class for hundreds thousands of students at public and private schools throughout the area – including the Chicago Public Schools.

To see if your school is still closed on Wednesday, click here for a list of school closings.

Although temperatures dipped to 6 below zero overnight at O’Hare International Airport, they were steadily rising Wednesday morning. By 7 a.m., the temperature was 1 below zero, and the forecast called for a high temperature of 15 degrees on Wednesday.

That warming trend should continue through the end of the week, with a high of 26 on Thursday, 37 on Friday and Saturday, and 38 on Sunday.

CBS 2’s Susanna Song reports school bus drivers worked throughout the afternoon and evening on Tuesday to make sure school buses would be ready to pick up kids on Wednesday.

Workers at the Sunrise School Bus company yards on the West Side started scraping away snow and thawing out buses around 3 p.m. Tuesday. Drivers put jumper cables and fresh batteries to work to get them started.

One worker at the Sunrise bus barn said it’s quite task to get the buses in drivable condition after sitting idle for more than two weeks.

“Diesel buses; the fuel, everything thickens up,” James said.

Students at the Chicago Public Schools and many suburban school districts have been off for the holiday break since December 19. Though most schools’ winter break was set to end this week, all local schools canceled classes Monday and Tuesday, due to heavy snow from last week, and extreme cold temperatures early this week.

That reprieve came to an end Wednesday morning, as schools reopened for classes after temperatures returned above zero.

On Monday, CPS Chief Executive Officer Barbara Byrd-Bennett said when schools re-open, children will be safe and warm.

“We will have building engineers in schools throughout day … to check on boilers, and to ensure that the heating systems are working for when students return to their classrooms,” she said.

In addition to normal classes, all regularly-scheduled after-school activities were set to resume on Wednesday. Makeup days to cover the missed days will be decided later.

Service also was returning to normal for public transit agencies. After dozens of trains were canceled on Monday and Tuesday, and many other trains were significantly delayed due to icy tracks, Metra was reporting far fewer delays early Wednesday.

By 8 a.m., the rail service reported few delays for the morning commute.

Inbound and outbound trains on the BNSF were experiencing delays up to 20 minutes because of freight train interference, switching problems and inclement weather, according to Metra’s website.

There were also delays for an inbound train on the Union Pacific Northwest Line, a few trains on the Union Pacific West Line, and the Milwaukee District West Line, due tue switching problems.

Meantime, the CTA was expecting normal service for buses and trains on Wednesday, and was reporting no significant issues during the morning rush. Many of its trains were delayed Monday and Tuesday due to problems with ice, and some buses were running behind schedule due to ice and snow on many city streets.

At Chicago’s airports, after hundreds of flights were cancelled from Sunday through Tuesday, airlines were hoping to resume somewhat normal operations on Wednesday.

Over the past three days, more than 4,000 flights were canceled at O’Hare, and nearly 500 were canceled at Midway International Airport.

On Wednesday, airlines at O’Hare canceled more than 180 flights, while airlines at Midway canceled fewer than 6.