Confirming the suspicions of first-borns everywhere, researchers found that the eldest child is the most intelligent.
Economists from the University of Edinburgh say the first-in-line has a 'mental edge' over brothers and sisters, outperforming them because they get more stimulation from their parents.
The study looked at data from 5,000 children - who were asked to complete reading and vocabulary tests every two years.
The results show that the eldest child achieves higher IQ scores from as early on as the age of one.
Published in the Journal of Human Resources, the project looked at the mental progress of children from pre-birth to the age of 14.
The birth order effect
The researchers claim that the study results could explain the 'birth order effect'.
This is when children born earlier enjoy better salaries, top jobs and more education.
Dr Ana Nuevo-Chiquero of the University of Edinburgh's School of Economics said:
Our results suggest that broad shifts in parental behaviour are a plausible explanation for the observed birth order differences in education and labour market outcomes.
What's more, previous studies have also shown the eldest sibling have more success in life. Research from the University of Essex suggests that first-borns are 16 per cent more likely to go to university than their siblings.
Feifei Bu, a PhD candidate at the university who led the study said:
What surprised me about the study findings is that the birth order effect is much stronger than the impact of gender in terms of attainment.
But for those that were not lucky enough to be born first, there is hope. It's been claimed younger siblings have an advantage in other areas.
In a study by the University of Cardiff, elder siblings were found to be more likely to be short-sighted. This could be down to the amount of time parents devote to educating them.
And in a YouGov study, research revealed that non-first-borns were more likely to say they are more funny, easy going and relaxed when compared with their elder siblings.
Family forces are at work
The University of Edinburgh study concluded that age itself may be "responsible" for the difference in characteristics. It claims:
Older children, having had more time to get on in life, are more likely to say they are more successful than their siblings.
It also suggests that 'family forces' are at work when new family members come along - suggesting parents move their attention to the new born - leaving first-borns to fend for themselves.
The research claims:
As evidence, elder siblings are more likely to feel more organised and able to prioritise their own lives.