This study aimed to test whether an online scenario-based learning activity increases student teachers’ self-efficacy and emotional, motivational, and cognitive classroom readiness before they start their first teaching practicum. Specifically, we explored whether the effectiveness of the intervention depends on the inclusion of expert teacher feedback and the opportunity to reflect on the scenarios. A total of 238 Australian student teachers (64.3% females, mean age = 23.84 years, SD= 6.64) participated in the study. The student teachers were randomly assigned to one of three experimental conditions: waiting-control group (scenario-based learning activity), intervention group 1 (scenario-based learning activity, feedback) and intervention group 2 (scenario-based learning, feedback, reflection). The findings from a path model indicated that both intervention types significantly enhanced cognitive classroom readiness. A significant effect on self-efficacy was found for intervention group 2. Overall, our research demonstrates the potential of an easy-to-implement online intervention in enhancing self-efficacy and classroom readiness.