We've seen lots of research on the effect of birth order on children — but what about birth spacing? A new study shows that spacing kids out may be good for them — or at least the older ones.
The Times highlights research by Notre Dame economists studying a sample of 5,010 sibling pairs. The researchers examined the siblings' math and reading scores on standardized tests administered between the ages of 5 and 18, and plotted those results against the number of years between the siblings. They found that more space between kids was correlated with higher scores for the older children — younger kids didn't do any better when they were far apart from their siblings, but they didn't do any worse either. Why does more space help older sibs do better on tests? Study authors Kasey S. Buckles and Elizabeth L. Munnich have some ideas:
[S]pacing does increase the probability that the mother reported reading to the child every day when the child was of preschool age. Likewise, the probability that there are more than ten books in the house is increased by spacing. Each year of spacing also results in a marginally significant decrease in the hours of television the child watched on weekdays as a preschooler. These results suggest that both time and financial investments in the older child may be increased by spacing.
The study authors also looked at spacing effect across socioeconomic classes — older siblings from the lowest-income families got the biggest benefit from space. Irrespective of income, though, their findings make a certain amount of intuitive sense. Older kids who get to be only children for several years receive that much more parental attention, and it's not a surprise that this sometimes translates into higher test scores. Of course, as the study authors remind us, they only looked at math and reading — they didn't test the kids' social skills, which could be improved by having a sibling at home from a young age.
They also didn't look at relationships between siblings. A big age gap can cut down on competition between kids, but it also means they're at very different developmental stages for much of their upbringing. My brother is five years younger than I am, and when we were growing up, that meant we rarely went to the same school, liked the same toys, or watched the same shows (except Doctor Who). We certainly played together sometimes, but I also tried to act like a third parent to him, something that made him mad and got me in trouble. I also tended to make a big deal of our age gap, describing my brother as "much younger" than me. Recently, however, a friend pointed out that now that we're both adults, five years isn't "much younger" anymore. A lot of our childhood dynamics have disappeared too — it's been many years since I tried to tell him what to do. I'm not sure if our spacing helped me do better in school, but I'd like to see how sibling age gaps effect people not just from 5 to 18, but beyond. Do the benefits to older siblings persist over time, or, like the gaps themselves, do they become less important as the years go by?