First-borns might score higher on measures of intelligence, because, at some point in their lives, they were only children who were the sole recipients of their parents’ attention.

Younger siblings might earn better grades, because they received mentoring from first-borns who already had to tackle certain subjects, the researchers say. Also, later born children might feel extra pressure to be competitive, and might try to out-do their older siblings in the hopes of gaining extra attention from parents.