Young children's friends are the people they play with most. These children become familiar and predictable. Later, by four years of age, children start to select friends who match their developmental skills, their activity levels and their temperament. This is the beginning of true reciprocal friendship.
But at the start of middle childhood, children's choices of friends are modified by group pressures. In a way, it's like the stock exchange: it's safe to invest in friends who will raise your status within the group, and risky to associate with peers the group does not respect.
This can break the hearts of six- and seven-year-olds whose close friends now abandon them. In one scenario, two children are best friends when alone, but then one shuns the other at school, where others are looking.
This age is also when bullying begins. Bullying has two faces: it can consist of direct attacks such as pushing, shoving, tripping someone up, stealing someone's possessions and taunting. This form is more common in boys through the primary school years.
Girls typically use less direct methods. They try to control others by putting conditions on a friendship, or restricting access to social events such as birthday parties. Some children seek to dominate a peer by dictating that the peer play only with them. Other tactics include talking behind people's backs, spreading rumours, and, these days, harassing them on social networking sites. These methods allow perpetrators to disguise their aggressive intentions.
There are three differences between bullying and aggression. The first is that bullying is systematic - repeated targeting of a child whom the group sees as weak. Aggression targets whoever is nearby.
The second difference is that bullying increases with age. Most bullies are socially skilled and can manipulate others into doing their bidding. They have high self-esteem because they value power.