In a study commissioned by the Government, the Institute for Fiscal Studies has found that pupils born over the summer are likely to fall behind children born at the beginning of the academic year.
The researchers say that the effect can last throughout their schooling, and in turn have an impact on GCSE results and their prospects at A-level and university.
They stressed the need for "urgent" action to tackle the problem of "summertime schoolchildren", such as weighting test scores in accordance with the age of the children sitting them.
The researchers also recommended increasing flexibility over when children start school, and when they proceed to the next stage of schooling. However, this would mean making more nursery education available.
They also supported a policy being piloted by the Government, which recommends letting younger pupils defer exams until they are ready to sit them.
Claire Crawford, one of the authors of the research, said that some children face a penalty "simply because they are unlucky enough to have been born late in the school year".
"This cannot be acceptable on either equity or efficiency grounds, and urgent steps must be taken to eliminate this inequity," the Telegraph quoted her as saying.
The study showed that 60.7 per cent of girls born in September achieved at least five A-C grades at GCSE, while only 55.2 per cent of girls born the following August reach the standard.
About 50 per cent of boys born in September would achieve five C grades or better in GCSEs, as compared to 44.2 per cent of those born at the end of the school year.
The researchers say that teachers and parents often mistake poor performance as a result of pupils' age for evidence that their children have special educational needs.
During the study, the factors that might be behind these differences, including the age at which children start school, the amount of schooling they receive before they take their tests, and whether they are among the oldest or the youngest in their class, were all examined.
It was found that "overwhelmingly, it is the age at which a child sits the tests that matters".
"It is crucial that account is taken of date of birth in determining progression in education beyond age 16," Lorraine Dearden, another of the report's authors, said.
"At the point at which a child leaves school, then of course actual qualifications must be used to reflect true levels of human capital. But when assessing whether pupils can continue in education, age-adjusted results must be used to avoid penalising summer-born children unfairly," Dearden added.
Schools Minister Andrew Adonis welcomed the study and said that measures were being put in place by the Department for Children, Schools and Families to overturn the trend.