Slick, icy roads and sudden white-outs often lead to school bus cancellations in the winter, but schools themselves are rarely closed to staff and students.

Every time there's a snow storm, Ontario residents take to social media to ask why the schools are still open if roads are unsafe for buses.

Most school boards told that schools are only closed if students and staff would be in danger by attending. The decision is made early in the morning by a team of administrators including the board's director and transportation staff.

In Toronto, approximately 90 per cent of kids either walk to school, take public transit or are driven by parents, so schools are rarely closed when buses are cancelled. Most of the students can still get to school as usual.

"However, if schools are closed, 250,000 students would not be able to go to school and thousands of parents are left to make childcare arrangements at a moment's notice," the Toronto District School Board website says.

"In some cases, it may not be possible and may result in children being left alone at home without supervision."

John Yan, the head of communications for the Toronto Catholic District School Board, told on Monday that only about one-third of that board's students depend on buses to get to school, because of the closer proximity of schools and accessibility to public transportation.

The TCDSB shares bus transportation services with the TDSB, and both only close schools when absolutely necessary for the safety of employees and students. During most storms in Toronto, students can still safely take transit or walk to school, he said.

Further west, the Peel District School Board looks at forecasts, police advisories and similar organizations in the area before making the decision.

For example, on Feb. 2, 2015, the board decided to close schools because provincial police advised non-essential traffic to stay off the roads.

Brian Woodland, PDSB director of communications, said the board is not only concerned about safety getting to school, but also about making sure they'll be able to get home.

Schools outside the city, including those in the Durham region, are more likely to close if a large percentage of students rely on school buses.

Durham District School Board Communications Manager Andrea Pidwerbecki told that some schools are virtually unaffected by bus cancellations, while others rely almost entirely on school buses.

"Typically, during inclement weather, the DDSB will cancel bussing for one or more transporting zones while the schools remain open," Pidwerbecki said.

"Weather conditions across the district can vary in terms of weather and road conditions. We work with local road managers and other partners in making any determinations."

The closure of schools is a separate process, which can be based on weather or mechanical issues within the building.

"If buses are cancelled it is up to the family to decide if conditions are safe to either walk or drive their children to school."