Experimental studies applying cognitive bias modification of attention (CBM-A) and interpretation (CBM-I) to reduce aggression have examined the effect of modifying each cognitive bias in isolation. In order to maximise the potential impact on both biases and symptom reduction, we examined whether a combined bias training procedure targeting both attention and interpretation biases (CBM-AI) in combination would be more effective than targeting interpretation bias (CBM-I) alone. University students (17–35 years) were randomly assigned to either a single session of CBM-AI training (n = 40), CBM-I training (n = 40), or a control condition (n = 40). Contrary to our expectations, participants showed an increase in adaptive attention and pro-social interpretation bias in all training conditions. Additionally, in none of the conditions, we found a significant change on self-reported or behavioural aggression. These findings suggest: (1) that the combined training did not have added effect over single interpretation bias training, (2) that training interpretation bias may lead to changes in attention bias, (3) that elements of the control condition unexpectedly, but interestingly, also affected attention and interpretation biases, and (4) single-session CBM procedures do not produce robust effects on self-report or behavioural measures of aggression in unselected samples.