Researchers have shown that breastfeeding causes children to do better at school. The research conducted by Oxford University and the Institute for Social and Economic Research, Essex University, found that as little as four weeks of breastfeeding for a newborn baby has a significant effect on brain development, which persists until the child is at least 14 years old.

The researchers matched each breastfed baby with one or more babies who were not breastfed, but who were similar in all other respects. Test scores in reading, writing and mathematics for the children at ages five, seven, 11 and 14 revealed a statistically significant difference between those who had been breastfed as compared with those who had not.

The research is published in a working paper 'The Effect of Breastfeeding on Children's Cognitive Development', which has yet to be peer reviewed.

Breastfeeding is more likely to be practiced by mothers who are of higher social class with a higher IQ. The researchers needed to demonstrate whether the relationship between breastfeeding and brain development was caused by the breastfeeding alone, or whether it was because mothers who breastfeed are likely to have more successful children anyway.

They used a rich dataset from the Avon Longitudinal Study of Parents and Children, which covers 12,000 children born in the early 1990s in the Bristol area. Babies were matched on a huge range of characteristics, including: their sex, gestational age, birth weight, their mother's age and marital status, parents' job status and education, and their home environment. Crucially, the researchers also used the parents' attitudes to breastfeeding as measured before birth.

Co-author Dr Almudena Sevilla-Sanz, from the Department of Economics and the Centre for Time Use Research at Oxford University, said: 'Comparing the test scores of groups of children matched in this way, we are effectively estimating the causal effect of breastfeeding. We find that breastfeeding does have a causal effect on children's cognitive outcomes. The difference is statistically significant across English, maths and science scores, and persists into secondary school. Indeed, there is some evidence that the effect tends to grow over time.