<p>The use of multiple informants in the evaluation of children’s aggressive behavior is considered a best practice, as it allows a more detailed and holistic understanding of this phenomenon. However, studies conducted exclusively within the scope of aggressive behavior functions are still scarce, and discrepancies between informants’ reports are common in studies that rely on proximal behaviors. Therefore, this study aimed to investigate the agreement between parent and teacher ratings of children’s reactive and proactive aggressive behaviors. To this end, elementary school children (<i>n</i> = 95, aged 7–10) were assessed using the Reactive and Proactive Aggression Questionnaire. The results showed that teachers reported higher levels of proactive aggression than parents. Nevertheless, reports from both informants were moderately to strongly related for both reactive and proactive aggression, with stronger agreement observed for reactive aggression. Sex differences also emerged: for girls, agreement was significant for both proactive and reactive aggression, whereas for boys, it was significant only for reactive aggression. The results, limitations, and directions for future studies are discussed.</p>