A study of 1,500 families across the UK suggests firstborn children are more ambitious when it comes to studying, and going on to college or university.
The study also found firstborn girls were 13% more ambitious than firstborn boys.
The study was carried out by Feifei Bu at the Institute for Social and Economic Research at the University of Essex.
Sibling Configurations, Educational Aspiration and Attainment followed 3,532 individuals (1,503 sibling groups) through the British Household Panel Study and Understanding Society.
Newsround sent Leah to a school to find out what kids there thought of their siblings.