Thousands of families with summer-born babies apply to education authorities for their child to enter reception class a year later. It comes amid fears that younger children do not perform as well as older classmates.
While some councils turned down more than half of requests, Northamptonshire County Council has accepted every request since 2016, a total of 142.
Education officers come to a decision after taking account of parents' views and information about the child's development.
Julie McCulloch, of the Association of School and College Leaders told the BBC, who compiled the figures,: "Some have a policy of automatically agreeing all requests, while others only agree requests where parents present very strong evidence.
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"We think there should be a consistent approach across the country."
Whether children who enter school later do better was thrown into doubt by a study published in May this year. Children born in England between April and August whose started school a year late did only slightly better in Year 1 tests than those who did not delay.
But Dr Claire Crawford, from the University of Birmingham, has researched the attainment of summer-born children who do not delay and said, in the early days, the gap in abilities between them and classmates is still quite wide.
She said: "We found the attainment gap was very large at the beginning of schooling as you might expect when the children are less mature, and the one year difference is a much bigger proportion of their lives."
The study also found that it was parents who were well-off that were more likely to request a delayed school start for their son or daughter.
Dr Claire Crawford, from the University of Birmingham, has researched the attainment of summer-born children at school.
She said: "Some parents may be more able to apply to defer their child or have access to the research than others."