Three complementary models of how peer relationship problems (exclusion and victimization) and aggressive behaviors relate to prospective levels of internalizing problems are examined. The additive risks model proposes that peer problems and aggression cumulatively increase risks for internalizing problems. The reciprocal risks model hypothesizes that peer problems and aggression transact over time and mediate the effects of each other on prospective internalizing problems. Last, the internalizing risks model proposes that, in addition to aggressive behaviors, prior internalizing problems also provoke peer problems that, in turn, further elevate risks for prospective internalizing problems. Data came from a sample of 453 low-income, ethnically diverse children in kindergarten to Grade 3 who were assessed 3 times over 1 school term (in January, March and June). Findings supported the internalizing risks model. Four key pathways were found to increase risks for internalizing problems by the end of the school year; 2 of these routes were rooted in aggressive behaviors, and 3 paths operated indirectly via levels of peer problems in the spring. Children who were initially aggressive became excluded by peers by the spring, whereas children who initially showed more symptoms of depression and anxiety became victimized by peers by the spring. In turn, both peer exclusion and victimization increased prospective levels of internalizing problems by the end of the school year.