A dual-factor model (DFM) of mental health conceptualizes complete mental health as both low levels of psychopathology and high levels of subjective well-being (SWB). Although middle adolescence (ages 14 to 18 years old) is associated with increases in symptoms of psychopathology and declines in SWB, further research is needed to understand how youths' membership in a DFM changes across multiple time points. This study analyzed the stability of a DFM for students enrolled in accelerated coursework, and the relationship between initial mental health status and immediate and distal academic outcomes (i.e., student engagement and grade point average). A sample of 328 students reported on well-being, symptoms of psychopathology, and engagement (affective, behavioral, and cognitive) during the 9th grade fall, 9th grade spring, and 10th grade spring. School records indicated grade point averages at the end of 9th and 10th grade. Findings indicated that approximately 53% of youth changed mental health status over time, frequently due to a simultaneous increase in psychopathology and decrease in SWB. Results from multilevel modeling indicated that, regardless of level of psychopathology, initial low levels of SWB significantly predicted lower academic performance and student engagement over time compared to complete mental health (i.e., high SWB in combination with low psychopathology). Given students' declining mental health across 9th and 10th grade, and the relationship between mental health and academic outcomes, educators should consider monitoring and fostering both positive and negative indicators of mental health during the start of high school.