TORONTO - Ontario's standardized tests are being rigged to boost student scores and back up the claim that kids are better off under the Liberals, Progressive Conservative Leader John Tory charged Tuesday as party leaders used the first day back at school to woo voters with their education plans.

Since the elementary reading, writing and math tests were introduced in 1997 under the previous Conservative government, the tests have gotten easier and students have been given more time to write them, Tory said.

Students are now allowed to use calculators during the test, which also skews the results, he added.

The suggestion the standardized tests have been rigged drew scorn from the agency that administers them.

"Any suggestion that the testing has been manipulated to improve results is not only false but it's a disservice to the thousands of dedicated and committed Ontario educators who have worked so hard to address the learning needs of their students,'' Charles Pascal, chairman of the board of directors for the Education Quality and Accountabililty Office, said in a statement.

"If there was even an attempt to compromise the independence of EQAO by the government, I would resign on the spot.''

At his own back-to-school event in Oakville, Ont., Premier Dalton McGuinty dismissed Tory's claim as simply "not true.'' But Tory said McGuinty's claims of improving student performance under the Liberals is undermined by the changing nature of the tests.

"That claim by Mr. McGuinty deserves an asterisk beside it,'' Tory said during a campaign-style stop outside an elementary school in Mississauga, Ont.

"You are not comparing apples to apples. If there have been changes in standards, changes in the way the tests are done, you can't necessarily say (scores) are going up one year to the next.''

Although the election campaign doesn't officially start until the writ is dropped Sept. 10, all three mainstream party leaders were wasting no time Tuesday courting parent voters and highlighting their education credentials.

"I'm here to celebrate the achievements that we have made,'' McGuinty said. "I'm here to encourage all those who continue to put their shoulders to the wheel to keep going. We're going in the right direction.''

Education Minister Kathleen Wynne, who will square off against Tory in a marquee battle for the Toronto riding of Don Valley West, said the provincial testing authority is responsible for how the tests are administered and is completely independent of the government.

The tests are a reflection of how well students are coping with the curriculum, she said. It only makes sense that students who use a calculator in class should be able to use one on the standardized test, Wynne added.

"You can see real improvement over the last four years,'' she said. "If we had been tampering with the tests, then the test scores would have been much higher.''

The number of Grade 3 students meeting the provincial standard in reading has jumped from 50 per cent to 62 per cent in the last five years while the number of Grade 6 students who met the provincial standard in the same subject jumped from 56 per cent to 64 per cent.

Marguerite Jackson, chief executive of the Education Quality and Accountability Office, which oversees and administers the tests, said the evaluations have changed somewhat over the last decade.

The provincial curriculum has changed so the test reflects that, she said. But the tests aren't easier now than they were a few years ago, nor is the testing authority in cahoots with the governing Liberals, Jackson said.

"Mr. Tory is misinformed,'' Jackson said. "The tests are very rigorous.''

Still, NDP Leader Howard Hampton said the standardized tests are -- and always have been --"political tests.'' They are less about helping students, teachers and parents and more about getting political parties re-elected to government, he said.

Teachers who have been hired to mark the tests say they've gotten easier -- with more multiple choice questions -- and are marked more leniently, said Hampton, who pledged an NDP government would scrap the tests entirely and use the $50 million budget to improve education in the classroom.

"This kind of standardized testing is a huge waste of money,'' he said. "I would get rid of this political test.''