The self-control literature emphasizes the importance of intervention programs to strengthen the self-control skills of school-age students. Accordingly, this study aimed to evaluate the efficacy of a self-control intervention program (SCIP) on school-age adolescents’ self-control and grit traits. In this quasi-experimental design study, an eight-session SCIP grounded in the process model of self-control was implemented in the experimental group with 24 students, whereas the control group consisted of 24 middle and high school students. Assignment to groups was nonrandom. The data were analyzed using a two-way mixed ANOVA. The findings suggest that SCIP can be a promising program for improving the self-control and grit of middle and high school students. School counselors and other school-based mental health providers can use the SCIP to promote self-control in their students, which is one of the goals of the ASCA National Model and the social-emotional curriculum.