But the debate over the impact of birth order gained new urgency this summer when the results of a new study were announced: Firstborns' IQs tend to be higher than those of their younger siblings.
Does that mean later-born kids are destined to be less accomplished and successful? Studies like this don't tell the whole story -- and neither do birth-order stereotypes. Here's how to bring out the best in each child:
What the latest study found
Norwegian scientists analyzed test results and birth data from more than 241,000 military conscripts and found that oldest children had an average IQ of 103, second children came in at 101, and third-borns were at 100.
Is that a big spread? It's not a difference you'd ever notice, but some researchers say it could mean the difference between getting into a top college versus a second-tier one.
What accounts for the difference? Nobody knows. There's speculation that eldest kids benefit from having their parents' undivided attention for a while -- until another swaddled bundle arrives home from the hospital, that is. Or it could be that moms and dads have especially big dreams for their first kid, and the child picks up on it. Another theory: Eldest children are given more responsibility and are expected to show their sibs the ropes, which builds brainpower.
Will this scenario play out in your family? Not so fast. Like all studies, this one has limitations:
* The study's Norwegian -- maybe there's something special in the lingonberries over there.
* The subjects were all male -- who knows if it's true for sisters?
* IQ numbers themselves aren't rock-solid. "Today's tests have a surprising degree of error," says Nathan Haselbauer, founder and president of the International High IQ Society. A score of 110, he says, means that your true score is probably between 105 and 115. And older IQ tests were even less precise than modern ones. "Since the Norwegian study used data as old as 1967, I'd say that trying to find meaning in the three-point gap it found could be nothing more than a wild goose chase," Haselbauer says.
* While small differences like the ones this study found are important spread across the entire population, they're likely next to meaningless within a family. Remember that the averages for everyone in this study -- firstborn and last -- were well within the normal range.
Parenting senior articles editor Deborah Skolnik doesn't feel less intelligent than her older sister...