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.
Newsround sent Leah to a school to find out what kids there thought of their siblings.
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I have one older brother and even though I don't like to admit it he definitely is the most ambitious of the two of us..
Merel, Amsterdam, The Netherlands
I think older siblings are not ambitious because my older sister has nothing she wants to aim for. She is not determined like me.
Keith, Leicester, England
I'm more ambitious than my brother and he is two years older than me. He is thirteen and I'm ten, yet I go for more things than he does.
Rebecca, Burtonwood, England
I don't think that it's true because I have a younger sister who is fourth born and she is much smarter than her older three siblings when they were her age.
Sarah, England, London
Yes, I do have older siblings but I think I'm the most ambitious in my family.
Lucy, Taunton, England
I have a big sister aged 16 and a little sister aged 7. I think that me and my bigger sister are the most ambitious siblings in our family.
Liam, Glasgow, Scotland
I'm a middle child and I'd definitely say I'm the most ambitious and studious from my siblings! So I'm afraid I don't agree with the study.
Zaira, Midlands, England
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.