TORONTO - About 79 per cent of Ontario high school students graduated within four or five years, Premier Dalton McGuinty said Monday.

That translates to about 16,500 more students graduating last year compared to the previous year, amounting to a two per cent increase, said ministry officials.

The governing Liberals have promised to raise the graduation rate to 85 per cent by next April.

McGuinty expressed confidence that he can hit that target, despite the steep climb required in the number of students earning a diploma.

"One of the things I've discovered about targets is that they act as powerful magnets for collaboration," he said from Don Bosco Catholic Secondary School in Toronto's west end.

"It gets my office on the ball, it gets the Ministry of Education on the ball, it gets the rest of the cabinet table on the ball. And we all say, 'OK, what do we need to do to help achieve this?"'

However, the province's graduation rate includes students who went back for a fifth year, in addition to those who earned their diploma within the usual four.

In 2008, only 69 per cent of students completed high school in four years, five years after the province eliminated Grade 13.

The most recent figure was not immediately available from the Education Ministry, which compiles the statistics.

American states are not allowed to include students who take more than four years to complete high school in their graduation rates unless the students are developmentally disabled or still learning English.

Other provinces use different ways to calculate graduation rates and some, including Alberta, P.E.I. and Newfoundland and Labrador, consider high school to start at Grade 10 instead of Grade 9.

Manitoba and Nova Scotia have similar programs to Ontario, and both measure students who complete high school in four years. Manitoba's most recent grad rate was 79 per cent, while Nova Scotia's was 85 per cent.

According to the ministry, more than 52,500 more Ontario students have earned a high school diploma since 2003-04, when the Liberals took office.