COLUMBIA, Mo. -

A school bus bound for Rock Bridge High School in Columbia left students standing in the rain Monday morning.

Kirk Powell contacted ABC 17 News when the bus failed to show up long after the scheduled 8:18 a.m. time. He said he had to drive his son to school after a conference call.

"I got him there at 10, so he was right at about an hour late," Powell said. "He missed his first class."

Powell's son was one of several at the stop on Laredo Trail and Saddle Ridge in Columbia's Thornbrook neighborhood. He said his son's tardiness had been excused for his first class.

Michelle Baumstark, community relations director for Columbia Public Schools, told ABC 17 News Monday afternoon the district had called on an unusual number of substitute bus drivers because of morning Music Extravanganza activities at the Hearnes Center.

Baumstark said the district had not planned on the overlap of getting students to those activities while picking up high school students because of the new start times.

She said district leaders would now look at future event start times to avoid overlap and avoid using that man substitute bus drivers.

" I don't want to beat them up," Powell said. "But at the same time, I don't want my kid standing on the corner freezing, it's going to be cold before long."

Stephanie Creech of First Student, based in Cincinnati, Ohio, said the company was still investigating what happened Monday. It would decide what action to take once the exact cause of the mishap was determined.

"We will take steps to improve performance going forward," she said. "The safety of all students we transport is a core value."

Columbia Public Schools and First Students said they had been contacting parents on the route Monday to apologize and discuss concerns.