They boast, challenge each other, and hurl insults. Rather than encourage communication, they disrupt it by changing the subject or interrupting. Their goal is to one-up each other, to hoist themselves up the hierarchy. They like body contact. By age 4, kids play with same-sex peers about three times more often.
Girls pull away before boys.
Maccoby pioneered research into gender segregation among kids, believing that boys and girls were growing up in separate cultures. Those cultural differences later play out in relationships, the workplace, and parenting. During her own research, ASU's Martin observed 40 children at the university's Child Development Lab. Every day for a couple months, she and her research assistants watched individual children, noting their activity and playmates. Most of the girls and boys spent less than 20 percent of their time with the opposite sex, she says.