Relational aggression is becoming increasingly recognized as a very prevalent behaviour amongst females, especially within school settings. Robust findings have supported N.R Crick and K.A. Dodge's Social Information Processing Model (1994) as being a useful model in explaining physical aggression amongst males. However, little research has examined the model with regards to relational aggression in females and research that does exist has shown inconsistent findings. The current study examined the fifth step of the model, Response Decision, in a sample of female adolescents. The four factors that have previously been identified as contributing to the response decision step were examined, including response evaluation, outcome expectancies, self-efficacy evaluation, and response selection. In view of suggestions made by W.F.Arsenio and E.A.Lemerise (2004), level of moral reasoning was also examined with regard to how relationally aggressive responses were evaluated. These factors were examined within hypothetical relationally aggressive peer situations in relationally aggressive, overtly aggressive, relationally plus overtly aggressive and non-aggressive participants. The results show that compared to non-aggressive and overtly aggressive females, relationally aggressive females show a bias in the four processes of the response decision step. Differences in levels of moral reasoning were also found between the different aggression type groups. Hence the findings provide support for Crick and Dodge's (1994) Social Information Processing model in explaining relationally aggressive behaviour. The findings are discussed with regards to their implications for educational settings.