Epidemiological studies indicate that as many as 1 in 5 young people will develop a mental health problem in any given year. Early detection and intervention are needed to reduce the impact that these conditions have—both for the young person and for the communities in which they live. This study reports the development of a new instrument aimed at helping identify students at risk of developing mental health difficulties. Rather than asking about the presence of symptoms of mental health conditions, the RADAR screening tool assesses a student’s balance of risk and protective factors associated with the development of mental health problems. The RADAR was evaluated with a sample of 838 participants in high school Years 7–12. A robust internal factor structure was revealed using exploratory and confirmatory factor analysis. Internal consistency was satisfactory for each subscale, ranging from .73 to .90 while the reliability for the total scale was .91. Retest stability, measured over a 12 month period, was found to be strong (r = .72). Convergent validity was demonstrated with reference to standard measures of depression and behavioral problems. It is concluded that the RADAR is a promising measure for helping mental health professionals and educators decide which students may be at risk of developing mental health problems.