Purpose: This study examined the effectiveness of a 12-week mindfulness curriculum for at-risk, urban adolescents. Of particular interest was whether participation in the intervention was associated with gains in self-regulation and self-compassion. Design/Approach/Methods: The analytic sample included 217 public high school students from thirteen 11th and 12th grade classrooms; 133 students received one dose of the program, 39 students received two doses, and 45 students served as a control group. The program was delivered by a trained mindfulness instructor who met with the classrooms once a week for 45 min. Adolescents completed self-report measures tapping self-regulation and self-compassion at pretest and posttest. Findings: Results indicated significant benefits of the intervention for adolescents' self-compassion among both intervention groups. The effect was larger among students participating for the first time (one-dose group) than for those who were participating for a second time (two-dose group). There was also evidence that the program supported self-regulation, as students in both intervention dosage groups maintained their levels of long-term regulation relative to their peers in the control group who reported a decline over time. Originality/Value: While both self-regulation and self-compassion were supported as mechanisms of change associated with mindfulness-based intervention, the effects of dosage differed across the two constructs. The impacts of timing and dosage need to be examined in future research to better understand the sustainability of program effects for adolescents.