A driver in Edmonton resigned after a three-year-old girl was left sleeping on her school bus Wednesday morning.

The child did not get off the bus when it arrived at Mother Theresa Elementary School in central Edmonton where the girl attends a preschool program.

When the bus returned two and half hours later, the little girl was still on board. 

"Police are confident that the little girl fell asleep. She probably slipped down on the seat a bit, so she was not visible, and she was asleep for the two and a half hours that the bus was not at the school," said Lori Nagy from Edmonton Catholic Schools.

The school's principal called police, and the female driver was interviewed. Police said they believe the child was not harmed and aren't pursing the matter any further.

Millie Smith, office administrator with RL Smith Transportation, said she is concerned that the driver did not check the bus to make sure everyone had gotten off.

"One of our daily routines is for the drivers to do a walkthrough after they've dropped off their students at the school," she said. "We will be meeting with our drivers over the next week to again go over this procedure."

Smith said the bus was parked at the driver's home, which is where drivers take their vehicles after they do a run.

Smith said the driver, who has been at the company since September, resigned immediately after the child had been found. 

The driver had passed all criminal checks.

But the school district says it has serious concerns about how the bus company handled the incident.

"Only 20 children could sit on that bus, and yet the bus was not checked," Nagy said. "Really, that is inexcusable."

Nagy said the school board's contract with its bus carriers stipulates that buses are checked to make sure every student has gotten off.

Nagy said that Edmonton Catholic Schools board will be looking at all the options to ensure this doesn't happen again, including possibly looking for another bus carrier.

Nagy said she doesn't know what steps the school took to notify the parents. She said that will be part of the board's investigation.