Intervention. All students received 30 minutes of introduction to the simulator including a short introduction to vaginal ultrasound examination. The simulator instruction was provided using a standardized template developed in the pilot study. Constructive feedback was provided when participants encountered problems that they wanted feedback on. The instructor was a clinician ultrasound simulation expert. The participants in the intervention group did not receive any continuous instructor support but were allowed to consult an instructor whenever the participants encountered a module that they could not pass. The total training time was two hours in both groups. Hence, participants in the dyad group received half the 'hands-on' time as the participants in the control group.