By Afua Hirsch, Social Affairs Editor
A new system of resits will require 11-year-olds in England to prove they are meeting minimum standards in maths and English if the Conservatives are returned to power in the General Election.
Under the Tory plan, any pupil who does not achieve a good pass in their English and maths Year 6 'Sats' will be required to resit the exam in their first year of secondary school.
The Conservatives say that it will make sure pupils who leave primary school unable to read, write or do basic maths will have caught up by the time they are 12.
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Education Secretary Nicky Morgan announced the measures in response to concerns that 100,000 children are still failing to reach the expected standard in numeracy and literacy by the end of primary school.
Ms 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."
Schools already receive a £500 "catch-up premium" for every child who does not meet the expected standard at the end of what in England is known as Key Stage 2.
But there is evidence that poorer children are still significantly under-performing compared to their more affluent peers, with only half as many children eligible for free school meals attaining five GCSEs compared to their classmates.
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Experts questioned how much extra support would be available as a result of the Tories' new pledge.
"It's pretty clear there's no new money attached to this, so what we are talking about for secondary schools is using the existing catch-up premium they get," said Jonathan Simons, head of education at the think tank Policy Exchange.
"But assuming that schools are already spending that money on something, they are going to have to do without extra resources."
At the Explore Learning centre in south London, where children attend classes in the school holidays to try to improve their performance at school, there was concern about the pressure on pupils.
"I would say it would potentially be useful, but it potentially could be just another opportunity for children to get anxious about another exam," said Kathleen Goodwin.
The announcement is the Conservatives' first significant education policy pledge since the election campaign began.
Labour said the policy failed to address the root causes of low attainment.
"This is a desperate attempt by the Tories to overshadow their failures on school standards," said Shadow Education Secretary Tristram Hunt.
"On their watch, 1.6 million pupils are being educated in schools that are rated lower than 'good' by Ofsted."