They're also planning to double the length of time it takes teachers to get a degree from one year to two years starting in 2015.
Former premier Dalton McGuinty made the promise just before the 2011 election campaign.
He pledged there would be no new spaces in teacher education programs.
It appeared that new Premier Kathleen Wynne was taking it a step further by cutting spaces, but the Liberals say it's the same thing McGuinty promised to do.
Education Minister Liz Sandals says there are about 9,000 admissions right now, which will be reduced to 4,500 each year after 2015.
Minimum time for classroom placements will rise to 80 days from 40 days, she said.
"That's because teaching has gotten way more complicated than it used to be," Sandals said. "And there's a lot more things teachers need to know about."
They'll also make changes to the teachers' curriculum to address diverse student needs and provide expertise in working with students who have mental health and addiction issues, she said.
"So what we're doing is we're modernizing the program."
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