Primary school children are being "set up to fail" by the government's new Sats tests, Labour's shadow education secretary has warned.
Labour frontbencher Angela Rayner said many teachers believe the new expected standard is "beyond the reach" of the majority of children as she launched a blistering attack on education secretary Nicky Morgan.
But Mrs Morgan accused Ms Rayner of peddling "mad conspiracy theories" after she suggested the government was trying to bring back the 11-plus "through the back door".
Leading an opposition day debate on the issue, Ms Rayner said: "Our children are being set up to fail. Almost half of England's 11-year-olds will now go on to secondary school being told by this government that they are failures.
"But the real failures are this government and in particular the current secretary of state for education, who pushed ahead with this flawed system despite all the warnings from the education profession that its primary assessment system was not fit for purpose."
Ms Rayner said separating children on the basis of Sats results and making them resit the tests "sounds to me like the dark days of the 11-plus" where children were "branded failures".
But Mrs Morgan hit back and said Ms Rayner's speech "captured everything that is wrong with the Labour Party at the moment".
"Mad conspiracy theories, deferring to the unions and zero answers to the problems facing this country," she said.
Although she rejects the idea that the tests were a failure, the education secretary admitted the roll-out of the new tests was "not as smooth as it could have been and for that we have apologised".
Mrs Morgan claimed Ms Rayner's speech could have "easily" been written by National Union of Teachers (NUT) acting general secretary Kevin Courtney – who called for the minister to resign on Sunday. She said it represented the final stage of Labour's transformation into the "parliamentary wing of the NUT".
Liberal Democrat John Pugh, MP for Southport said: "Sometimes in these debates, criticising the government can be quite difficult. But when the minister describes the debacle of Sats as a great success, criticising government policy gets relatively easy – it's like shooting fish in a barrel."