Lib Dem leader Willie Rennie has accused the Education Secretary of being like Donald Trump by being “in denial” over P1 assessments.
Mr Rennie said John Swinney and the US President were like “two peas in a pod” as he hit out at claims the tests had been implemented without any difficulty.
Mr Swinney branded the suggestion “ridiculous” and said it did little to help “decent discourse” within the Scottish Parliament.
The exchanges took place at Holyrood, where Deputy First Minister Mr Swinney was standing in for Nicola Sturgeon during First Minister’s Questions.
Mr Rennie put it to Mr Swinney: “The Education Committee said he was confused, teachers said they had no real value, parents in his own constituency boycotted them, the teachers’ union wanted them scrapped, and Parliament instructed John Swinney to stop – that’s national testing for five-year-olds.
“Yet on Tuesday he claimed the test had been implemented without any difficulty whatsover.
“On the very same day in London, Donald Trump claimed he only saw cheering crowds. Two peas in a pod, both in denial.
“Isn’t the truth that the national testing saga is symbolic of his performance as Eductation Secretary?”
The Deputy First Minister responded: “I think that ridiculous question is symbolic of Willie Rennie’s leadership.
“It really, I don’t think, serves decent discourse in this Parliament for Willie Rennie to characterise his questions like that. He can say what he likes to me, it’s water off a duck’s back to me, but I don’t think it helps his credibility one iota.”
Mr Swinney said he had based his earlier comments on the fact that 650,000 assessments took place in around 3,500 schools during the first year of the implementation of a “complex” IT project.
He said he would say more about the assessments in a statement to Parliament on Tuesday.
“I want to make sure teachers have access to resources that will inform their judgment about the progression of young people through the education system,” he added.
Mr Rennie called for the tests to be scrapped and asked if Mr Swinney has met the First Minister’s expectations when she appointed him as Education Secretary.
“Yes,” he responded.