Social emotional learning (SEL) is being promoted as a universal approach to preventing mental health problems and promoting academic success. Indeed, SEL curricula have been shown to produce positive outcomes for students. However, many studies indicate that SEL curricula work the best for students who at baseline need it the most. These findings raise questions regarding whether SEL programs are associated with universal benefits across the full spectrum of students. Considering this, the purpose of this study was to utilize a theoretically-informed approach to constructing groups of students according to their baseline status on mental health-related measures and examining the degree to which a widely adopted SEL program is associated with positive outcomes for each of these sub-groups of students. Specifically, the dual continua model of mental health was used to create four categories by assessing functioning on two intersecting dimensions (well-being and psychopathology). As part of a larger study, data from teacher surveys measuring student mental health functioning (N = 7,185) of early elementary age students were collected, and this dissertation examined how student functioning changes on both continua in response to receiving universal SEL instruction from the Second Step� curriculum. Chi-squared tests and generalized logistic regression modeling with mixed effects were performed to analyze data and examine differential treatment outcomes based on student functioning at baseline. Results indicated that universal effects were not as strong as expected across dual continua groups, and students with low well-being at baseline benefited the most. Students with high well-being did not demonstrate significant treatment effects. Future implications about the utility of the dual continua model and universal SEL programs in schools, as well as potential directions in research is discussed.