When it comes to kids who beat up other kids or destroy their stuff or just generally act aggressive, research has a lot to say about their parents’ relationship, household income, food habits, and even the number of books in the house. But one thing it hasn’t said much about is the effect of a step or half-sibling — which is odd, because prior to kindergarten, siblings are who most kids spend most of their time with. New research from the University Of Michigan Institute For Social Research takes a closer look at how these kids impact childhood behavior, and results aren’t warm and cuddly.
The researchers used data from the Early Childhood Longitudinal Study-Birth Cohort of 6,550 kids, whose primary parents were interviewed when their child was 9 months, 2 years, 4 years, and during their first year of kindergarten. In the study, parents scored their kids for aggressiveness on a scale ranging from 0 (never) to 28 (very often), and after household income, race, gender, and birth order were controlled for, kids with step or half siblings scored significantly higher. It’s already pretty well established that a kid who grows up without one of their biological parents is more likely to act aggressively toward other kids, so maybe this latest research is sort of obvious: If a kid’s step or half sibling is kind of a dick, that kid is more likely to be a dick in return.
Another interesting bit from the study: There are way more step and half siblings than previously thought. One-in-8 U.S. kids will live with one by the time they reach 18, and 60 percent of kids born to unmarried parents have one by age 10. It is also apparent from the study that fathers seriously help mitigate bad behavior, so congratulations on your powers of persuasion — if you’re living in one of these complex family arrangements, you’re going to need them.