Research by the Institute for Fiscal Studies (IFS) found pupils born in August are 6.4 percentage points less likely to achieve 5 GCSEs at grades A* to C than those born in September.
They are also two percentage points less likely to go to university at age 18 or 19, and one percentage point less likely to attend a Russell Group institution, though these detrimental effects did not persist into adulthood.
Those born in the summer also did go on to earn the same as those in the autumn and had the same levels of employment, health and happiness, the study says.
“Very large differences in attainment between children born at the start and end of the academic year…affects the post-compulsory education options open to them,” said the report’s co-author Claire Crawford, IFS programme director.
Age-adjusted scores should be used by admissions tutors to determine entry, as well as for streaming children within school, the study recommends.