The planned cuts are included in the government's 2015-16 education funding guide, which was obtained by the New Democrats and calls for permanent savings of up to $500 million by 2017-18.
"Lets face it," Sandals told reporters. "We do have a deficit, so we're going to have to look at every government program and make sure that we're managing it efficiently."
The real issue is that the number of pupils is declining, added Sandals.
"So yes, there may be from year to year sometimes a slight decrease in funding, but the funding per pupil actually continues to rise," she said.
The document, copies of which were released by NDP education critic Peter Tabuns, says the plan is challenging as it represents a potential reduction of one to two per cent in total revenue.
"These cuts will hurt an education system that's already hurting from being underfunded," said Tabuns. "It could mean ballooning class sizes, teacher layoffs and even more school closures."
Sandals didn't dispute the funding guide's authenticity, and said there are over 600 schools in Ontario that are more than half empty, and some will be closed.
"We want to make sure that money is being spent on educating the students who are there and not on funding empty seats," she said.
The New Democrats said the planned reduction flies in the face of Premier Kathleen Wynne's pledge in the legislature just four months ago not to cut education funding.
"Her budget promised increased funding to school boards," Tabuns told the legislature. "She's on the record promising no cuts to schools, and yet the Ministry of Education is spelling out $500 million in cuts to our classrooms and says annual increases are things of the past."
The Progressive Conservatives said school closings would inevitably be in small-town and rural Ontario, where schools are often the hub of the community, and warned that shutting down some of them would not result in huge savings.
"Shutting them down and busing kids 15, 20 or 30 kilometres away, I don't think is an option," said PC education critic Garfield Dunlop. "And I don't think it's going to save her $500 million either."
Sandals said education funding this year hit $22.5 billion, an increase of 56.5 per cent, or over $4,000 per pupil, since the Liberals were elected in 2003.
"We have increased spending in education more than any other government has ever done," she said.
The education minister also dismissed the idea of eliminating Ontario's Roman Catholic school system and combining it with the public system, which the provincial Green Party has advocated. The Liberals will abide by the Constitutional requirement for Ontario to have a separate system for Catholic education, added Sandals
"The economic arguments are not strong arguments for school board amalgamation," she said.
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