This study investigated whether a mental health promotion program delivered by primary school teachers to prevent internalising problems in children had any impact on the teachers' job-related affective wellbeing. Teacher job related anxiety and job-related depression were measured before teaching the Aussie Optimism program, and after implementation at 12 and 24 months. Schools and teachers were randomised to one of three groups: Aussie Optimism with Teacher Training; Aussie Optimism with Teacher Training and Coaching; or the Usual Care control group, which implemented the regular Western Australian Health Education Curriculum. In all three groups, teachers taught lessons to promote student self-management and interpersonal skills during the last two years of primary school. Teachers in schools in the control group received training in Aussie Optimism after the first year of intervention. Data was collected from 405 primary school teachers in 63 government primary schools. Multiple hierarchical regression analyses showed partial support for the hypotheses, with teachers in the Training and Coaching intervention group reporting significantly lower levels of job-related anxiety at the 12-month assessment and depression at both the 12- and 24-month assessments when compared to teachers in the Usual Care control group. There were no significant differences between teachers in the Training only group and the control group after intervention.