Ostracism (i.e., being ignored/excluded) can cause intense emotional reactions that detrimentally impact mental and physical health. Adolescents may be particularly susceptible to these negative consequences due to brain maturation and changing social priorities. To better understand how neural mechanisms of ostracism vary across development (i.e., age, puberty), the current study employed a pictorial adaptation of Hudac's (2019) Lunchroom electroencephalography (EEG) task in a sample of 84 adolescents (aged 10-14 years). Results indicated unique effects across event-related potential amplitudes, including a reversed pattern (greater sensitivity to inclusion) for the P1, the "classic" ostracism effect (greater sensitivity to exclusion) for the N2, and classic effects when modulated by puberty for the P3. Source estimation identified different neural networks that were likely driving sensitivity to exclusion (e.g., amygdala, SCG, and IFG) or inclusion (e.g., ACC, cingulate, fusiform, insula, SPL, STG). Further, sensitivity to exclusion increased over pubertal development for P3 amplitude but over age for amygdala and IFG. Sensitivity to inclusion decreased over age for P1 amplitude and inclusion sensitive regions. The current study emphasizes the utility of using paradigms that isolate neural processes associated with ostracism while controlling for participant involvement.