The issue of summer-born children is in the news again, with new research from the Institute for Fiscal Studies (IFS) which claims that children born in the summer in England are at an academic disadvantage throughout school. By contrast, babies born in September are more than three times less likely to be viewed as "below average". You can read the full text of the report - entitled Does When You are Born Matter? The Impact of Month of Birth on Children’s Cognitive and Non-Cognitive Skills in England - by clicking here.
This topic has been examined several times in recent years. For further reading try Cambridge University's Birthdate Effects: A Review of the Literature from 1990-on, the NFER's The Influence of Relative Age on Learner Attainment and Development, or the DfE's 2010 report Month of Birth and Education.