Stability and change of bullying over a four-month interval was examined in 516 middle school students (grades 6-8). The stability coefficient was .65 for the entire sample. There was a significant increase in bullying behavior from Time 1 to Time 2 for 6th grade students; no significant change in bullying was found among 7th or 8th graders. For 6th graders, a greater confidence in using non-violent strategies was associated with less bullying at Time 2, while beliefs supportive of violence and misconduct, less positive adult influences, and more negative peer influences were associated with greater likelihood of bullying at Time 2. Higher levels of impulsivity, anger, and depression were also associated with greater levels of bullying over time. Several explanations for the increase in bullying behaviors among 6th graders are discussed and linked to intervention efforts.