Pupils in England who get poor results in their Sats tests at the end of primary school will face a resit in secondary school if the Conservatives form the next government.
It would mean 100,000 pupils taking a new test in English and maths during their first secondary year.
Prime Minister David Cameron promised parents “more rigour, zero tolerance of failure and mediocrity” in schools.
Labour has emphasised the quality of teaching as the way to raise standards.
“This is a desperate attempt by the Tories to try to overshadow their failures on school standards,” said Labour’s shadow education secretary, Tristram Hunt.
Nick Clegg, the Liberal Democrat leader and deputy prime minister, attacked Conservative education policy for an obsession with a “tiny handful” of free schools at the expense of “how you properly finance 24,000 schools across the whole school system”.
Policy guide: Education
This election issue includes funding for schools, university tuition fees and early years education.
The test resit plan from the Conservatives, which would be implemented next year, is aimed at making sure that pupils have not already fallen too far behind at the beginning of secondary school.
Pupils who did not get good grades in the Sats tests taken by 11-year-olds in primary school would have to retake a test during their first year after moving up to secondary school.
In last year’s tests, 79% of pupils achieved the expected grades in reading, writing and maths.
The Conservatives argue that, too often, pupils who have slipped behind by this stage never catch up. Among those who fail to make the grade at the age of 11, they say only 7% go on to get the benchmark measurement of five good GCSEs, including English and maths.
There is already support for secondary schools of £500 per pupil who has struggled in their primary school tests.
The resit would be a standardised test in maths and English, marked by teachers rather than external examiners. There could be up to two retakes, in the spring or summer terms, and the number of pupils who had failed the retakes would be published as part of the league table data.
Pupils with special needs would not have to take the resits.
‘Could be useful’
Mr Cameron said: “There is no job that doesn’t require English and maths, and this is about making sure every child gets the best start in life and that our country can compete in the world.”
Education Secretary Nicky Morgan said: “We know that the biggest predictor of success at GCSE is whether young people have mastered the basics at age 11. That means if we fail to get it right for young people at the start of secondary school they’ll struggle for the rest of their time in education.”
Malcolm Trobe, deputy general secretary of the Association of School and College Leaders union, said many secondary schools already had strategies and tests to make sure that pupils moving up from primary had the basic skills for the secondary curriculum.
He said such a “standardised test for use in Year 7 to help teachers assess the progress of those students could be useful”.
But he said that such tests “must not be bureaucratic to administer or increase workload.
“It is important that the results of these tests are diagnostic and used to support the work of the teachers and do not become yet another performance indicator on which to measure schools.”
‘Cradle to college’
For Labour, Mr Hunt stressed the importance of teacher quality as the key to raising standards and accused the Conservatives of failing to make enough improvements.
“On their watch, 1.6 million pupils are being educated in schools that are rated lower than ‘good’ by Ofsted. And as a result of David Cameron’s unqualified teachers policy, more than 400,000 pupils are being taught by unqualified teachers.
“Labour has a better plan for education. We will ensure that every teacher is qualified or working towards qualified teacher status and introduce a new master teacher status to raise the standing of the profession. That is how we improve education for every child, in every classroom,” he said.
Mr Clegg has emphasised the importance of protecting funding for the school system.
He promised that “one of our front-page manifesto commitments will be to protect the education budget from nursery to 19-year-olds, from cradle to college”.
The Liberal Democrat leader cast doubt on funding for free schools, when “maintained schools in the maintained sector are crying out for extra investment”.
That “just seems to me to be an irrational use of scarce resources, in effect for ideological reasons”, said Mr Clegg.