This paper reports an investigation into Australian primary school teachers' knowledge and confidence for mental health promotion. Questionnaires were delivered to 1397 teachers. In-depth interviews were held with 37 teachers. Quantitative results showed that half to two thirds of teachers felt efficacious and knowledgeable about selected components of mental health promotion. Independent judgments by staff about students' mental health status concurred with students' scores on the Strengths and Difficulties Questionnaire in about 75% of cases, indicating a good level of staff awareness about students' mental health status. Exposure to the KidsMatter Primary mental health promotion initiative was associated with improvements in teachers' efficacy, knowledge and pedagogy, with small to medium effect sizes. Qualitative analysis indicated that teachers' subject-matter and pedagogical knowledge were heavily reliant on curriculum resources. Implications of the findings for the implementation of school-based mental health promotion initiatives are discussed. (Contains 5 tables and 3 notes.)