New research from the American Psychological Association compared 90 sibling pairs. Results showed that while both the oldest and youngest siblings generally believed they were the smartest (naturally, sigh…), the oldest sibling tended to score higher on aptitude tests.
Still, while the oldest sibling scored better, the data showed that the youngest’s efforts often surpassed the oldest’s, with generally higher grand point averages than the firstborn. One reason younger siblings may do worse on aptitude tests is because they are used to receiving extra help and attention for schoolwork.
There was also another study that discovered younger siblings were “more outgoing, sentimental, forgiving and open to new experiences than their older siblings.” (This study also found that firstborns were smarter.)