This study examined the feasibility and potential efficacy of the Resilience Education Program (REP), a Tier 2 school-based internalizing intervention. REP represents a hybrid intervention approach, incorporating both small-group cognitive-behavioral instruction and a check-in/check-out reinforcement-based mentorship program. A randomized controlled trial research design was employed, in which students (grades 4–7) were randomly assigned to treatment (n = 21) or waitlist control (n = 17) groups. Given the early phase of REP research, the trial was underpowered but capable of generating unbiased effect size estimates that could inform subsequent fully powered efficacy trials. Outcomes of interest included student internalizing concerns (as reported by teacher and self-report measures) and the change mechanisms by which REP was theorized to influence internalizing concerns (i.e., emotional control and social support). Primary MANCOVA findings indicated that although non-statistically significant, between-group differences in youth self-reported and teacher-reported internalizing concerns corresponded to large effect sizes (ηp2 = .15–.19). A follow-up MANCOVA inclusive of change mechanism variables was also non-statistically significant, but representative of a large effect (ηp2 = .38). Following trial completion, REP implementers positively rated the acceptability of the REP intervention as a Tier 2 intervention for addressing internalizing concerns in the school setting.