A new study finds having a smart older brother or sister has a knock on effect that makes younger siblings do better.

The research looked into the progress of 220,000 children over four years.

It found that younger children benefit most when their sibling helps them with homework, or even when they copied their older brother or sister.

But it does not work in reverse - with improvement of younger siblings not found to benefit the eldest child.

The study by the University of Essex in the UK is the first to investigate a so-called multiplier effect on younger brothers and sisters.

It found that for every extra exam grade achieved by an older sibling, the younger brother or sister's marks increased by around 4%.