Studies show that the oldest child in a family typically scores higher on IQ tests than the children born after him or her. Each level down in birth order corresponds to diminishing IQ. In other words, the third-born scores lower than the second, the fourth-born lower than the third. Plus, the IQ-factor transfers over to academic aptitude. The differences aren't huge, which should provide some consolation for those third or lower in the family line-up.
In contrast, younger siblings tend to be more extroverted, forgiving, agreeable, and sentimental than their older sibs. Some studies have found that younger siblings function better in social situations, are more independent, and enjoy risk-taking more. There's some evidence that younger siblings are funnier. The latest studies even show that younger siblings perform better in school, grade-wise, in spite of the lower IQ and aptitude.
Learn more about sibling ranking and mental health with this natural health podcast!