Social dominance goals have been conceptualized as orientations toward powerful and prominent positions in the peer group. Although previous studies have identified social dominance goals as one of the main motivations behind bullying, few studies have disentangled the time-invariant (average level) from the time-varying (year-to-year) effects of social dominance goals. The present study simultaneously examined the time-invariant and time-varying associations between social dominance goals and bullying, along with the moderating effects of classroom bystander behaviors (reinforcing the bully and defending the victim). A Chinese sample of third graders (n = 615, 46.5% girls, Mage = 9.29 years, SD = 0.40) and fourth graders (n = 559, 44.9% girls, Mage = 10.31 years, SD = 0.40) in four schools was surveyed three times (in May 2018, May 2019, and June 2020). Social dominance goals and bullying were self-reported. Classroom reinforcing and defending were assessed by averaging peer-reported reinforcing and defending scores for each classroom at each time point. Three-level models revealed significant time-variant and time-invariant effects of social dominance goals on bullying in classrooms with relatively low levels of defending behavior. These results suggest that both persistent and temporary social dominance goals might motivate children to engage in bullying, but peers’ defending behaviors mitigate this tendency.