Bus cancellations in a western Alberta school division have caused a dramatic drop in attendance, the deputy superintendent says.

Frigid temperatures have led to widespread cancellations in the rural Wild Rose School Division, which has 4,800 students and 18 schools stretching between Drayton Valley and Caroline.

"We've got some schools — at the beginning of the polar vortex when buses weren't running — that are having close to the zero per cent [attendance mark]; probably just a small handful of students that have made it in," deputy superintendent Greg Wedman told CBC News.

"But those numbers have been steadily increasing at many of our schools as the vortex has dragged on."

That's likely because parents are finding other ways to get their children to school, Wedman said. But some of the bus routes are more than an hour long, meaning parents have to choose between a lengthy commute and keeping their kids at home.

The cancellations started on Feb. 1, and have included days where all 76 routes were called off, Wedman said. On Tuesday, 42 routes were cancelled.

Since Feb. 1, there have been days where all 76 bus routes in the division were cancelled. (CBC News)

The northern region of the school division uses contracted busing, while the southern region uses divisional busing, Wedman said. The Wild Rose School Division and its contractors consider cancelling routes when temperatures fall to –35 C or a wind chill makes it feel like –40.

"It is a tough thing for us trying to make that decision because we're balancing between student safety and ... their learning," Wedman said, noting that safety comes first. "We're going to err on the side of caution, but it gets tougher as this polar vortex carries on."

'How do they expect to get the children caught up?'

Shawna McGinn's sons were out of school on Tuesday. They attend H.W. Pickup Junior High and Frank Maddock High School in Drayton Valley, and have missed several other days due to route cancellations and a teachers' convention.

Contractors have too much say in whether bus routes get called off, as cancellations interfere with learning, McGinn said.

"There's no other form of public transportation that comes around and picks kids up in the farmland," she said.

She's worried students are falling behind.

"I know teachers try to to use their time wisely, but now their time has really been constricted because of these snow days," she said.

"How do they expect to get the children caught up on education?"

Some teachers have shared learning materials online, and students will likely have more homework once they're back in school, Wedman said.