Families with two children tend to do better at school, according to new research.

A study by the Institute for Social and Economic Research at Essex University found that children with one younger brother or sister have better educational results than those in bigger or smaller families.

The findings, published this week, run contrary to the popular belief that families with an only child will see their son or daughter achieve better school results.

It is well recognised that children from larger families are found to do worse than children from smaller families, and children lower down the birth order do worse than those higher up the birth order.

Researchers analysed exam results from the 1960s and 1970s and found that elder siblings in two-child families got better O-level results than both larger and small families.

Children who were the child in a family did, however, perform slightly better in non-scientific subjects at some ages.

The author of the study, Maria Iacovou, suggests that the better performance could be down to the way adults explain maths to youngsters and that it may be easier for children to explain number concepts to each other.

She found that the next best achievers were the oldest of three siblings and the younger sibling of two children, followed by the middle of three, youngest of three and eldest of six.

In larger families, the oldest child was usually the highest achiever but the age gap between children was also significant.

To view the research click here.