This study examined how changes in cumulative peer victimization are associated with depressed mood and suicidality among adolescents over time, as well as whether certain protective factors (e.g., school mattering) moderate these associations. Middle and high school students (N = 2,539) from a small city in the Great Plains responded to five surveys across three years. Multilevel logistic regression analyses were conducted to examine within-person changes in cumulative peer victimization (i.e. number of victimization types experienced), depressed mood, suicidality, and several protective factors. Within-person increases in cumulative peer victimization were associated with within-person increases in depressed mood and suicidality. The effect of cumulative peer victimization on both depressed mood and suicidality was attenuated at higher levels of school mattering, highlighting the importance of this protective factor against depressed mood and suicidality.