Differences during teenage years can cause conflict in friendships and therefore lead to their early dissolution.
"Adolescents are most likely to enjoy successful, long-term friendships with those who share similar traits," said Brett Laursen, professor at Florida Atlantic University in the US.
The study looked at 410 adolescents involved in 573 friendships. All friendships originated in the seventh grade, and researchers followed the participants from grade seven through grade 12.
Fewer than one fourth of the friendships that started in the seventh grade were maintained across the next school year, and fewer than one in 10 friendships that started in the seventh grade survived the transition from middle school to high school.
Only one percent of friendships that began in the seventh grade continued to the 12th grade. The strongest predictors of friendship dissolution were differences in sex, differences in the degree to which children were liked by other children, differences in physical aggression and differences in school competence.
By far the strongest predictor was differences in sex; other-sex friendships were almost four times more likely to dissolve than same-sex friendships.
The next strongest predictor was differences in physical aggression, followed by differences in school competence, and differences in being liked by other children. Rates of dissolution increased by 25 percent to 43 percent for each unit of difference on these variables.
"We knew from previous studies that children prefer similar others as friends," said Laursen.
"Now we know why differences are bad for friendships. It causes conflict, interferes with cooperative activities and shared pleasures. It creates circumstances where one friend bears more costs, such as the friend who is less aggressive or gets more benefits like a friend who has lower social status than the other," Laursen added.