Delaying a summer-born child's entry to primary school has little impact on attainment, research suggests.
Children born in England between April and August, whose start in Reception was put back a year, did only marginally better in Year 1 tests, according to a government study.
The number of applications to councils for delayed entry has risen sharply. Head teachers' unions want clearer guidance on whether delayed school entry for summer-born children works.
Department for Education researchers looked at results achieved in the Phonics Screening Check, taken by pupils at the end of Year 1.
Pupils whose school start was delayed a year in 2014 and 2015 scored on average 0.7 marks higher than other summer-born children. The researchers say the difference is not statistically significant.
Pupils who were not summer-born outperformed both the delayed and normal admission summer-born pupils.
The analysis also found parents with higher incomes were significantly more likely to request a delayed school start for their child. It also found the majority of applications, 74%, were from white British families.
Children in England usually start school in the September after they turn four but parents of children born between 1 April and 31 August can request to delay entry for a year.
Typically, this would mean a child starting school in Year 1, forfeiting Reception year. If a parent wishes to delay their child's admission to school until compulsory school age, at five, and be admitted into Reception, a request needs to be made to their local authority, for their child to be admitted out of their normal age group.
Councils are required to make a decision in the child's best interests, taking account of parents' views and information about the child's development.
Pauline Hull, of the Summer Born Campaign which has called for more flexible admissions, welcomed the report but said "the most important comparison is how much better these children are faring having started school at age five, rather than age four, and the DfE research does not address this.
