Children's changing ideas about friendship follow a three-stage sequence, confirmed by both longitudinal and cross-sectional research:
(1. Friendship as a Handy Playmate (about 4 to 7 years). Preschoolers understand something about the uniqueness of friendship. They say that a friend is someone "who likes you," with whom you spend a lot of time playing, and with whom you share toys. But friendship does not yet have a long-term, enduring quality. Children at this stage say that a friendship can dissolve when one partner refuses to share, hits, or is not available to play.
(2. Friendship as Mutual Trust and Assistance (about 8 to 10 years). In middle childhood, friendship becomes more complex and psychologically based. Friendship is a mutually agreed-on relationship in which children like each other's personal qualities and respond to each other's needs and desires. Once a friendship forms, trust becomes its defining feature. School-age children state that a good friendship is based on acts of kindness signifying that each person can be counted on to support the other. Consequently, older children regard violations of trust, such as not helping a friend who needs help, breaking promises, and gossiping behind a friend's back, as serious breaches of friendship. And rifts cannot be patched up simply by playing nicely after a conflict, as preschoolers and young school-age children do. Instead, apologies and explanations are necessary.
(3. Friendship as Intimacy, Mutual Understanding, and Loyalty (11 to 15 years and older). When asked about the meaning of friendship, teenagers stress three characteristics. The most important is intimacy, or psychological closeness, which is supported by mutual understanding of each other's values, beliefs, and feelings. In addition, more than younger children, teenagers want their friends to be loyal—to stick up for them and not to leave them for somebody else. As friendship takes on these deeper features, adolescents regard it as formed over time by "getting to know someone." In addition, they view friends as important in relieving psychological distress, such as loneliness, sadness, and fear. Because true mutual understanding implies forgiveness, only an extreme falling out can terminate a friendship.