All of the characters in Lord of the Flies are young schoolboys. They try to exist without the rules of adult society which would normally govern their behaviour. As with any group, some of the boys emerge as leaders and others become followers. Some behave well, most behave badly. A few demonstrate wisdom and maturity, while others become little better than savages.
The boys mostly seem to come from upper middle class backgrounds. It was common practice at this level of society for children to attend single-sex preparatory schools (prep schools) and then go on to a place at a fee-paying public school. Many children would live away from home as boarders - Ralph falls into this category. Jack and Simon attend a choir school and again seem to have the same reasonably privileged backgrounds as the other boys.
The one exception is Piggy who seems to come from a different class and has had a different upbringing, meaning that, despite his obvious intelligence, he is treated as an outsider. In the novel, the boys start by trying to create a civilised democratic society, organised along the lines they would be familiar with. This, however, very soon falls apart.