The impact of month of birth on child development

Research published by the IFS in 2007 examined the effects of school starting age on educational attainment, and found large and persistent effects. This project was designed to investigate further. It had two main aims:

1. To identify the impact of month of birth on the development of a range of skills and behaviours, including cognitive, non-cognitive, behavioural, social and emotional skills, and smoking, drinking and anti-social behaviour.

2. To identify the best school admissions policy – in terms of all-round skill development and overall behaviour, as well as educational attainment – for a child born towards the end of the academic year. 

The researchers used data from the Millennium Cohort Study, the Avon Longitudinal Study of Parents and Children, and the Longitudinal Study of Young People in England.  


Relative to children born in September, children born in August, on average:

  • Are 6.4 percentage points less likely to achieve 5 GCSEs or equivalents at grades A*-C (53.7% vs. 60.1%).
  • Are 2 percentage points less likely to go to university at age 18 or 19, and 1 percentage point less likely to attend a Russell Group institution.
  • Have lower confidence in their academic ability and are less likely to believe that they control their own destiny (locus of control) as teenagers.
  • 5.4 percentage points more likely to be labelled as having mild special educational needs at age 11 (12.5% vs. 7.1%).
  • More likely to engage in risky behaviours such as underage smoking at younger ages.
  • 1 percentage point less likely to obtain a degree.

In terms of what drives these differences, researchers concluded that: 

  • Age at test matters most. This means that children born in August end up with worse exam results, on average, than children born in September simply because they are 11 months younger when they sit national achievement tests
  • By contrast, we find that the age at which children start school and the amount of schooling they receive prior to the test explain very little of the differences in test scores. 
  • National achievement test scores should be age adjusted to account for the fact that children born at different times of the year have to sit the tests when they are different ages.
  • These age-adjusted scores should be used to calculate school league table positions, to determine entry to schools that select on the basis of ability and potentially also to assign pupils to ability groups within schools.
  • They should also be used to assess whether a pupil can continue into further and higher education. But when pupils leave school, they should take with them their non age-adjusted grades, to ensure that employers can be confident that pupils have achieved a particular absolute standard.
Project details



Dr Claire Crawford, Professor Lorraine Dearden, and Ellen Greaves, Institute for Fiscal Studies

Grant amount and duration


1 October 2009 - 31 March 2013

Education Committee


Starting school has been the subject of a recent Education Committee 'evidence check'

Read the oral evidence 

Watch the evidence session