Student wellbeing is of central concern for parents and teachers and for state and national governments. Policies on wellbeing are now articulated within all educational systems in Australia. Effective enactment of policy depends in part on the suitability of judgements made about students' mental health. This paper investigates teacher and parent/caregiver assessments of students' mental health based upon data from the evaluation of the KidsMatter mental health promotion, prevention and early intervention pilot Initiative in 100 primary schools across Australia. Goodman's Strength and Difficulties Questionnaire (SDQ) was completed by parents/caregivers and teachers of almost 4900 primary school students in KidsMatter schools, The SDQ was developed as a brief mental health screening instrument and is widely used in many nations, including Australia. A second measure, the Flinders Student Competencies Scale (SCS), which was specifically developed for this study, canvassed the five core groups of indicators of students' social and emotional competencies identified by the Collaborative for Academic, Social and Emotional Learning (CASEL 2006), namely, self-awareness, self-management, social awareness, relationship skills, and responsible decision making, as well as students' optimism and problem solving capabilities. This second measure was also completed by the students' teachers and parents/caregivers. A third measure was based on a non-clinical assessment by teachers and school leadership staff, who identified students in their school who were considered to be 'at risk' of social, emotional or behavioural problems. The first focus of this paper investigates how closely the three measures of identification of the mental health status of students correlate. The second focus of this paper investigates relationships between teachers' and parent/caregivers' ratings using the SDQ and the Flinders SCS. Results indicate that significant associations were found between the three measures of students' mental health. This suggests that non-clinical ratings, by teachers and leadership staff in the school, can provide one means of identifying students 'at risk', according to comparisons with the SDQ and the Flinders SCS. In triangulating the three sources of measurement, the authors provide a detailed picture of the mental health status of primary school students in the 2007-2008 KidsMatter schools. This paper provides a national snapshot of the mental health status of Australian primary school children. It also contributes to the growing body of literature examining the psychometric characteristics of the SDQ in the Australian setting, and to alternative measures for assessing student mental health in school settings. [Author abstract]