Research on loneliness has demonstrated it to be a common experience during both childhood and adolescence. It is also an experience that varies both as a function of children's and adolescents' social lives and of their psychological characteristics (Asher et al., 1990; Hymel et al., 1983). However, the study of loneliness prior to adulthood has reached a point at which it could benefit from theoretical models regarding the factors and mechanisms contributing to loneliness at different ages. This chapter points to areas that need to be addressed by such theories, and it outlines a developmental theory of the sources of loneliness in childhood and adolescence.

In the course of developing a theoretical model, we address the following questions. First, because theories of loneliness have often been based on a particular understanding of what it refers to, we discuss a number of issues that affect the definition of loneliness. Second, several possible models of the relationship between social deficits and loneliness are considered. Third, the chapter discusses evidence regarding the emergence of loneliness, the cognitions and experiences associated with loneliness in childhood and adolescence, and the kinds of social relationships and relationship provisions that are valued at various ages. On the basis of these, a stage model is proposed. Fourth, these stages are used as a framework for suggestions regarding developmental changes in the skill deficits and the other emotions providing routes to loneliness. They are used to identify experiences at each stage that may produce lasting vulnerabilities to loneliness.