Some say learning should be purely through play in the early years
A review of two key goals on literacy levels among young children in England has been announced - two months before they were due to come into effect.
Ministers wanted all five-year-olds to be able to write simple words and make attempts at more complex ones.
They also wanted them to be able to write their own names and begin to use simple sentences, sometimes with punctuation, by September 2008.
But evidence suggests only 46% can do the first, and some 30% the second.
Government education adviser Sir Jim Rose has been asked to consider, as part of his primary review, how appropriate these aims are for children at around the age of five.
It will also look at evidence showing when it is realistic for children to achieve them and how best to ensure children progress well between reception class and the first full year of primary.
The announcement comes after a panel of experts set up to advise on education policy for the under-fives was reported to have demanded radical changes to the targets, which they described as "overly ambitious for most children".
The goals were due to come into force in September as part of the Early Years Foundation Stage (EYFS) curriculum which provides a framework for early learning and the care of children from birth to five.
Ministers argue that the framework does not prescribe the way that childcare providers should operate day to day, but does contain "early learning goals" which children should be helped towards.
However, critics say it is too prescriptive and encourages a "tick box" approach from providers.
Children's Minister Beverley Hughes said: "We have always said that we will keep the EYFS under review, which is why I have asked Sir Jim Rose to look at two of the early learning goals on children's literacy at around the age of five, and report on how well they support a smooth transition into Key Stage 1 of primary school."
The Open EYE education campaign has been running a petition on the Downing Street website which has more than 7,000 signatures.
It suggested the EYFS could harm children's development, restrict parents' freedom of choice in childcare and education and place unnecessary bureaucratic burdens on those who care for young children.
Dr Richard House of the campaign said: "Just because some children can be drilled into meeting essentially arbitrary literacy targets at age five says nothing whatsoever about whether they are developmentally appropriate.
"There is simply no existing evidence that these goals are appropriate for five-year-olds, and plenty of evidence to the contrary - so the government is effectively playing grossly irresponsible Russian roulette with our young childrenís early learning."
Liberal Democrat children's spokeswoman Annette Brooke said the announcement was long overdue.
She said: "The new curriculum risks imposing a tick-box mentality upon the early years workforce and ministers should instead focus on driving up the quality of early years provision.
"The implementation of the whole framework must now be carefully monitored. Inspectors who understand early learning and the ways in which different types of setting can aid a child's development need to be used to ensure there is quality control."
She tabled a parliamentary motion raising concerns about the prescriptive nature of the Learning and Development Requirements of the Early Years Foundation Stage.
It also noted that children must be provided with a solid foundation in socialisation, listening and speaking skills, and fine motor skills before proceeding to the demands of reading and writing.
And shadow families minister Maria Miller said ministers' approach to early years just involves more and more bureaucracy and a complicated process of jumping through hoops to favour a fortunate few.
"The focus should be on making sure trained professionals are in place to help young children with reading and writing."