Extant research has produced conflicting findings regarding the link between social fearfulness and prosocial behavior, with some studies reporting negative relations and others reporting null effects. Furthermore, these studies have focused predominantly on toddlerhood, and few have examined prosociality between peers. The present study investigated whether the link between social anxiety and a prosocial behavior (i.e., providing encouragement) varied depending on interpersonal and situational factors (i.e., one's familiarity with a peer, the level of support sought by a peer, respectively). We tested this question using a multimethod approach, which included an ecologically valid stress inducing task and dyadic design with a sample of 9- to 10-year-olds ( N = 447). Results revealed that social anxiety was related negatively to providing encouragement among familiar and unfamiliar dyads. In familiar dyads, however, this main effect was qualified by an interaction with the level of support sought by one's peer. Compared to those low in social anxiety, children high in social anxiety provided relatively less encouragement in response to higher levels of support seeking from their peers. The findings are considered in relation to theorizing regarding the effect of overarousal on children's prosocial behavior.