Objective. To test the hypotheses that classroom and simulation-based crew resource management (CRM) training interventions improve teamwork attitudes and behaviours of participants and that classroom training combined with simulation-based training provide synergistic improvements. Design. A randomized controlled trial. Setting. Area Health Service in New South Wales, Australia. Participants. A total of 157 doctors, nurses and midwives randomized into one of four groups,consisting of three intervention groups and a control group. Intervention. One-day CRM-based classroom course; one-day CRM style simulation-based training or classroom training followed by simulation-based training. Main Outcome Measures. Pre- and post-test quantitative participant teamwork attitudes, and post-test quantitative trainee reactions, knowledge and behaviour. Results. Ninety-four doctors, nurses and midwives completed pre-intervention attitude questionnaires and 60 clinicians completed post-intervention assessments. No positive changes in teamwork attitudes were found associated with classroom or simulation training. Positive changes were found in knowledge (mean difference 1.50, 95% confidence interval (CI) 0.58-2.43, P = 0.002), self-assessed teamwork behaviour (mean difference 2.69, 95% CI 0.90-6.13, P = 0.009) and independently observed teamwork behaviour (mean difference 2.30, 95% CI 0.30-4.30, P = 0.027) when classroom-only trained group was compared with control; however, these changes were not found in the group that received classroom followed by simulation training. Conclusions. Classroom-based training alone resulted in improvements in participant knowledge and observed teamwork behaviour. The study found no additional impact of simulation training.