COLUMBIA, Mo. -

Columbia Public School officials said the first day back to school on Tuesday went smoothly.

First day enrollment was just more than 18,000, up 42 students from last year.

But CPS Superintendent Peter Stiepleman said that could still change over the next week because of late enrollment.

Right now, Stiepleman said they're keeping an eye on class size.

"After Labor Day is when we'll typically know what our normal is and so there are some schools where we have a class size of 27 in fourth grade," he said. "We're monitoring to kind of see, you know, is that going to stay there or are those numbers going to go down and they may be as small as 16 in some of our schools."

Stiepleman said those numbers are average.

The biggest Tuesday morning challenge was a few late buses, but other than that, officials said things went according to plan.

Officials told ABC 17 News earlier this month there was concern that the Jefferson Middle School wouldn't have air conditioning for the first week of school.

But that problem was taken care of just in time.

"We were concerned, but I give total credit to our buildings and grounds, our facilities guy," Stiepleman said.

This was also the first year Battle High School had a senior class. Stiepleman said that change also went into effect without any problems.