Social withdrawal occurs when an individual chooses to self-isolate in the presence of social company. While frequently correlated with being isolated by the peer group and peer victimization during childhood and adolescence, social withdrawal differs from peer isolation in that the reason for solitude is internal to the individual. Social withdrawal can serve an adaptive function when an individual feels socially threatened; however, some children develop a maladaptive version that results in consistent displays of social withdrawal across a range of social contexts. The development of such a phenotype carries costs from an early age; for example, toddlers who are behaviorally inhibited and shy often fail to develop age-appropriate levels of social competence during the elementary school years. Over time, these costs continue to mount, ...