Reunion behavior following stressful separations from caregivers is often considered the single most sensitive clue to infant attachment patterns. Extending these ideas to middle childhood/early adolescence, we examined participants' neural responses to reunion with peers who had previously excluded them. We recorded event-related potentials among nineteen 11- to 15-year-old youth previously classified on attachment interviews (11 secure and 8 insecure-dismissing) while they played a virtual ball-toss game (Cyberball) with peers that involved fair play, exclusion and reunion phases. Compared to secure participants, dismissing participants displayed a greater increment in the N2 during reunion relative to fair play, a neural marker commonly linked to expectancy violation. These data suggest a greater tendency toward continued expectations of rejection among dismissing children, even after cessation of social exclusion. In turn, the link between self-reported ostracism distress and neural signs of negative expectancy at reunion was moderated by attachment, such that self-reports were discordant with the neural index of expectancy violation for dismissing, but not for secure children.