This quasi-experimental pretest/posttest study using the School Counseling Self-Efficacy Scale examined whether school-counseling-specific supervision increased self-efficacy related to school counseling best practice. The study included supervision of 24 practicing school counselors using the School Counseling Supervision Model framework. Supervision groups had significant increases in self-efficacy scores compared to nonparticipants (p = 0.02), with a medium-to-large effect size (d = 0.62). Findings suggest that school-counseling-specific supervision can increase school counselor self-efficacy related to professional practice.