This study addresses the lack of research on the effectiveness of two major treatments for an adolescent sample. Both mindfulness and relaxation training are two major interventions that can be utilized to improve symptomology for aggression, disruptive behavior, anxiety, depression, perceived stress, as well as for the improvement of self-concept and academic performance. The focus of this study is to compare the effectiveness of mindfulness and relaxation training in a non-clinical sample of adolescents. It was hypothesized that the participants in the mindfulness group would have greater decreased levels in all facets assigned with the exception of self-concept and academic performance which would increase than the relaxation training and control groups. The participants in the relaxation training group were hypothesized to have a greater change than the control group. The present study also aimed to assess whether the underlying mechanisms of mindfulness and relaxation training were cognitive and physiological, respectively. Participants were student volunteers from general education classes at a public high school. They were randomly assigned to a mindfulness treatment, relaxation training, or inactive control group. Participants were given outcome measurements pre- and post-treatment to evaluate the impact of these interventions on anxiety, disruptive behavior, depression, stress, and self-concept. The participants in the treatment groups were also given measures to assess the underlying mechanisms of both mindfulness and relaxation training. At two-month follow-up they were asked if their academic performance had improved since beginning the study, but the follow-up was ultimately dropped due to low sample size. The results yielded no significant difference between relaxation training, mindfulness, and the inactive control for depression, anxiety, anger, disruptive behavior, stress, and self-concept. Further, the results yielded no significant difference in the underlying mechanisms of mindfulness of relaxation training. Although the current study yielded no significant results, this study emphasizes the importance of utilizing effective treatments and the implementation of brief treatments for adolescents.