The collision on Nov. 12 sent the school bus into a tree at the side of a home while the minivan landed upside down in the driveway. (Erin Collins/CBC)

A Calgary school bus driver crossed the centre line trying to pass a minivan, causing a collision that sent dozens of children to hospital, police allege.

The bus driver, Krista Donovan, 38, has been charged with driving carelessly, driving left of the centre line, and operating a commercial vehicle that had not been inspected under daily trip inspection requirements, police announced Thursday.

The driver of the minivan, Katherine Gamble, 33, has been charged with driving with a learner's permit without proper supervision by a qualified person.

The school bus and a minivan were both travelling eastbound at Ninth Street and 78th Avenue N.W. on the morning of Nov. 12. Police said the bus smashed into the minivan as the driver of the smaller vehicle was trying to turn left onto Ninth Street.

"The collision has occurred when she's gone into the opposing traffic lane to pass a vehicle that's turning left. Bottom line is you can't do that when you are driving a vehicle," said Sgt. Graeme Ramsay of the Calgary police traffic unit.

The collision sent the school bus into a large spruce tree at the side of a home, while the minivan landed upside down in the home's driveway.

Mechanical problems played no part in the crash, Ramsay added.

All 36 children on the bus were taken to the Alberta Children's Hospital, where some were treated for minor injuries. The two drivers were treated at Foothills Hospital, also for minor injuries.

Prior to the start of any trip and at the end of every shift, school bus drivers in Alberta are required to conduct a walk-around examination of the vehicle, and complete a written report based on the daily inspection.

First Student, the school bus company, defended the driver Thursday, saying she did what she thought was right at the time.

"We believe that the equipment had a fuel problem and that she, in that moment in time, thought that she didn't have brakes and that she took a course of action to protect her students, herself and the general public," said Steve Phillips.

"We know [now] that she had brakes, and the police inspection has confirmed that, we just think, her initial impression was that she didn't, and she reacted to that fact."