Pressure is growing to block plans to bring forward the effective school-starting age to four.
Government advisers have warned against the change, saying it could damage the social development of summer-born children and cause some to be misdiagnosed as having special needs. This would mean the abolition of staggered entry at reception level.
Opponents of the move, including members of the government's own early- education advisory group, hope to influence Sir Jim Rose, whose review into the primary curriculum will produce a final report later this term.
In an interim report published last term, Sir Jim called for all children to start reception in the September after they were four - a practice already widespread but not required by law. If ministers accept it, the change would begin in 2011.
But Professor Tina Bruce, a member of the advisory group, said she was surprised that the only rationale for the change was that it would improve children's communication, language and literacy development - just one of the six early-years development areas.
"I'm concerned that summer-born children, particularly boys, will suffer because the early-years curriculum sees six other areas of development as equally important - personal, social and emotional development, for example, is absolutely crucial."
Research also suggests that summer-born children are nearly a fifth more likely than others to be misdiagnosed as having special needs because of their struggle to keep up with classmates (see panel, right).
Bernadette Duffy, another member of the advisory group and head of the Coram children's centre in central London, said that reception classes did not need to abide by the small staff:pupil ratios compulsory for nurseries with four-year-olds.
"It's a long day and a busy day, especially if you are trying to keep up with children a year older than you," she said. "My anxiety is about a child's ability to cope with a more formal environment."
Members of the group are due to meet Sir Jim in the next few weeks. His interim report cited evidence that summer-born children were more likely to know the alphabet by the end of reception if they had been in school since September. It said the "more high quality pre-schooling (either in nursery or reception) that children receive, the better".
But others argue that nursery and reception are not the same.
Richard House, a member of the Open EYE campaign for less formal early- years education, said: "In theory, reception teachers follow the same curriculum as nursery staff, but in reality it isn't the same because of the pressure from local authority targets."
Sir Jim told The TES he was unlikely to change his mind about the start date, but there would be much more on reception classes in the final report. He also has to decide whether, at the end of reception, children should be expected to write their name and simple sentences.
"I think reception can be more tailored to individual children - and it should be," he said.
Summertime living, pages 26-27
Leading article, page 40
Summer-born children are up to 18 per cent more likely to be identified - possibly wrongly - as having special educational needs by the end of key stage 2.
This is according to the effective pre-school and primary education 3-11 project, which followed 3,000 children in that age group.
The researchers, from Oxford, London and Nottingham universities, said: "It is possible that teachers are not taking the differences in developmental status within a year into account adequately. This suggests that more assessments need to be age-normed so that immaturity is not mistaken for learning difficulty."
They found 36 per cent of autumn-born children were identified as having SEN compared to 45 per cent of summer-born children.
The Institute for Fiscal Studies in its report on summer-born children discovered that at seven, they score on average one level lower in the tests.
It found that at age 11, children were more likely to be recorded as having less severe, non-statemented special educational needs if they were born in the summer. They also discovered that by the age of 16, the identification of SEN did not seem to be linked to birth date.