How long does it take to make a friend? Think about your closest friend. In one study, it took roughly 50 hours together to move from acquaintance to casual friend. An acquaintance is someone you know a little. A casual friend is not as close as a close friend. In a study of grown-ups, a close friend took more than 200 hours of time together. That is the study's number for a close friend.

Babies know the faces they have seen. They show signs of being selective about who they spend time with. A baby can also react when another child is upset. Friends are not only for people. Female baboons form close bonds with other females in their troop. A troop is a group that lives together. A bond is a strong tie between two animals. Selective means choosy.

At first, very young kids play near each other and do not do much together. As they learn to talk, their play becomes more interactive, which means they do more with each other. Some kids who are not yet in school have one particular friend. Groups of friends can start to form too. A particular friend is one special friend. Interactive means doing things together.

These kids often prefer to play with kids of the same gender. Kids are more likely to be friends if they like the same things. Kids in school learn to deal with disagreements with friends. Gender means being a girl or a boy. Interests are the things you like.

Older kids in school start to form friendships that last and that help them. By middle school, friends tell each other private things. The word for that is confide. So friendship looks different in the older grades. Supportive means that friends help each other. Lasting means it stays.

Words to know

• acquaintance: someone you know
• interactive: doing things together
• confide: share private thoughts
• troop: animal group

The short version

Friendship grows with time together. In one study, it took roughly 50 hours together to move from acquaintance to casual friend, and a close friend took more than 200 hours, according to one study of adults. Babies respond to familiar faces, and by middle school friends confide in each other.

Quick facts

• Babies respond to familiar faces and show signs of being selective about who they spend time with.
• Preschoolers may have one particular friend, and groups of friends can start to form.
• In one study, it took roughly 50 hours together to move from acquaintance to casual friend.
• A close friend takes more than 200 hours of time together, according to one study of adults.
• By middle school, friends confide in each other.