BACKGROUND AND OBJECTIVE: Despite the crucial role of oral health literacy (OHL) in improving oral health outcomes, structured educational interventions targeting adolescents remain limited. This study aimed to assess the effectiveness of a school-based intervention in enhancing OHL among female students. METHODS: This randomized controlled field trial was conducted with 140 female secondary school students in Gorgan, located in northern Iran. Four public schools participated in the study, with two schools randomly assigned to the experimental group (n = 70) and two to the control group (n = 70). The data collection tool was the valid and reliable Test of Oral Health Literacy in Adults (TOHLA), which consists of four domains: cognitive, behavioral, media, and communicational. Following the pre-test, essential needs assessments were conducted. Subsequently, the experimental group received training in four 45-minute sessions, delivered by a team of dentists and the researcher. The training methods included lectures, question-and-answer sessions, practical demonstrations (using models), and educational video clips. Participants were also provided with pamphlets and PowerPoint slides as educational media. Two months after the educational intervention, a post-test was administered to all students. The collected data were analyzed using SPSS Version 16. The statistical tests employed included the McNemar test, ANCOVA, paired t-test, independent t-test, and Chi-square test. RESULTS: The intervention significantly improved the total OHL score, as well as its cognitive, behavioral, media, and communicational domains in the experimental group (P < 0.001). The control group showed a slight, yet significant, improvement only in the behavioral domain (P = 0.009), with no significant changes observed in the other domains. CONCLUSION: The study confirmed that a school-based educational intervention significantly improved oral health literacy (OHL) among female students. Significant increases were observed across all OHL domains in the experimental group, highlighting the effectiveness of structured interventions in promoting oral health awareness and behaviors among adolescents. While the study confirmed the intervention's effectiveness, it was limited to female students; future research should explore diverse populations and examine long-term effects.