RUTH Davidson has demanded an urgent review of the central pillar of Scottish schools education after the country’s worst ever results in international rankings this week.

The Tory leader said Curriculum for Excellence was now “on probation” and threatened to withdraw her party’s support for it, shattering the Holyrood consensus around the reform.

The 2015 Programme for International Student Assessment (Pisa) found the performance of Scots 15-year-olds in reading, maths and science had all declined or stagnated since 2012.

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At First Minister’s Questions, Nicola Sturgeon said she took full responsibility for the results.

They were “not good enough”, but further reforms, including a review of school governance designed to give schools more control, were underway to improve them, she said.

However Ms Davidson said: “The single biggest education reform under this SNP government has been Curriculum for Excellence and nobody here can simply brush aside the fact that since it has come in standards have fallen.

"So I'm telling the First Minister that our ongoing support for Curriculum for Excellence cannot be taken for granted. I believe that this entire project should be put on probation.

“There's a simple question that I ask, and I ask it in all sincerity: If standards are going down because of it, why are we sticking by it?"

Introduced in 2010 with the support of all parties, CfE is designed to make children “successful learners, confident individuals, responsible citizens, and effective contributors”, through a flexible curriculum covering 3 to 18 year olds.

However it has been criticised for being vague and woolly, as well as excessively bureaucratic.

Ms Sturgeon responded by quoting Tory education spokeswoman Liz Smith from the previous day in parliament, when she said the principles behind CfE were “absolutely right” and that there was “unanimous agreement within the parliament that it is the right way”.

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Ms Davidson accused the SNP of mouthing “bland platitudes” while standards were falling.

Ms Sturgeon said: "The results of the Pisa survey earlier this week are not where I want us to be, they are not good enough and I am determined that we take the action that will lead to improvement."

She highlighted improvements including a record number of exam passes in Scottish education and a higher percentage of young people going into positive destinations.

There was also the government attainment fund to narrow the gap between rich and poor children, the introduction of standardised assessments, measures to simplify the curriculum and the ongoing review of school governance.

She said: "These are hard, concrete, tangible actions."

Scottish LibDem leader Willie Rennie listed more than 20 countries placed higher than Scotland in the education rankings, including South Korea, Denmark, Ireland and Poland.

Demanding an explanation of "what has gone wrong," he said: "After 10 years of SNP rule, we are not even as good as England any more."

He said "complacency has been oozing out of ministers for a whole decade" while they "presided over the worst results ever".

Mr Sturgeon said: "I hope that the whole Parliament will get behind us, because some of what we are going to do over the next period will be controversial and some of it will run into resistance. At that point, it will be interesting to see whether the Opposition parties are behind us on these things or not."

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In an unusual move, education secretary John Swinney later criticised Ms Davidson, saying: “The Pisa results made for uncomfortable reading - but in difficult times, leaders do not abandon their principles, retreat and run for cover. Sadly, Ruth seems less interested in pupils’ education and more interested in pursuing the next cheap headline. Her attack on CfE reveals a lack of substance and of political resilience. It does her no credit at all.

“The Scottish Government will remain firm in our beliefs and listen, not to the turn-and-run Tories, but to our international advisers who have told us to be urgent in what we do, but patient about results. We will stay the course.”