Ontario will cut the number of new teachers who graduate every year in half and increase the length of time it takes them to complete a degree, The Globe and Mail has learned.

The move is aimed at curbing the growing glut of would-be teachers who cannot find work in their field – not only in Ontario, but in several other regions of the country.

It is also designed to keep Ontario-trained teachers competitive with their counterparts in other provinces and countries, who follow longer courses of study.

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The change, which is set to roll out by September, 2015, is expected to be announced Wednesday by Education Minister Liz Sandals and Training, Colleges and Universities Minister Brad Duguid. The length of teachers college will double from one year to two, with an increase in the amount of time teachers-in-training spend on classroom instruction.

The government will keep the number of college spaces at 9,000, but, with the extra year, each cohort will contain only 4,500.

Sources with knowledge of the government's plan said Queen's Park is tailoring the training system to the realities of the job market.

The Ontario College of Teachers certifies 11,000 new teachers every year, of whom roughly 7,500 come from faculties of education within the province.

But an OCT survey of 2011 graduates from Ontario education faculties and U.S. border colleges found that one-third were unable to find jobs in their field – a dramatic rise from just 3 per cent in 2006. In fact, many new teachers today cannot even find supply-teaching assignments.

The oversupply of teachers is most acute in Ontario, even as applications to teacher training programs have fallen sharply in recent years. But other provinces – notably British Columbia and Nova Scotia – have faced a similar conundrum, producing far more teachers than are needed to fill available jobs.

Last year, B.C. had at least 2,700 teachers jockeying for just 800 positions, and the number of opportunities coming open is not expected to rise for years.

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A report last fall from the government of Nova Scotia predicted that while the province will need an average of 281 new teachers each year until 2017-18, it is producing more than 900 annually.

Longer training courses for teachers are the norm in the rest of Canada, with most programs requiring three or four semesters. In some places, such as Alberta, students can enter teachers college without a previous degree, but must complete a four-year course of study.

Teachers trained in some overseas systems, with whom Ontario graduates will compete for jobs, also spend longer in school. Ontario's added year will help students in the program "acquire skills that are important in addressing the needs of our kids," such as special education, a source said.

Mr. Duguid would not confirm his plans Tuesday, saying only: "We are making an announcement tomorrow and it does involve the teachers."

But one source said the concept hasn't substantially changed since 2011, when the Liberals first embraced the idea. At the time, the government said the second year would allow in-class placements for student teachers to be expanded.

At the time, critics questioned some aspects of the plan. Student leaders pointed out that teachers-in-training would be required to fork over an extra year's worth of tuition, even though the government will not be spending extra money on the expanded program.

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Teachers' unions, meanwhile, argued that since the province's colleges train teachers to focus on specific subjects or age groups, it was not possible to simply say that longer degree programs would mean a better education.

The government can make the change by revising the Ontario College of Teachers Act to require that new teachers have a second year under their belts.

The province consulted with teachers colleges, school boards and teacher groups on these changes last year.

The OCT is expected to work with faculties of education to accredit the changes.