This study examined the longitudinal stability and dynamics of group membership within the Greenspoon and Sakflofske's dual-factor model of mental health. This expanded model incorporates information about subjective well-being (SWB), in addition to psychopathological symptoms, to better identify the mental health status and current functioning of youths. Participants included 730 seventh- and eighth-grade U.S. middle school students. Four groups of students were identified: flourishing (i.e., high SWB and low psychopathology), vulnerable (i.e., low SWB and low psychopathology), symptomatic but content (i.e., high SWB and high psychopathology), and troubled (i.e., low SWB and high psychopathology). Analyses of stability of group membership revealed varying levels of stability, with flourishing students demonstrating the highest stability. Analyses also revealed that social support variables yielded meaningful predictions of changes in group membership. Implications for professional practice are discussed. (Contains 10 tables.)