Introduction: Oral health is an essential component of overall quality of life; however, the prevalence of dental caries in Indonesia remains high, particularly among elementary school children, partly due to inadequate toothbrushing skills. Various digital educational innovations, including mobile health applications and augmented reality (AR)-based interventions, have demonstrated positive effects on oral health education and behavioral change. Nevertheless, evidence regarding the effectiveness of the HI Bogi AR-based application, especially in improving children’s toothbrushing skills, remains limited. Therefore, this study aimed to analyze the effectiveness of the augmented reality-based HI Bogi application in improving toothbrushing skills among elementary school children using a quasi-experimental design. Methods: This study employed a quasi-experimental design with a one-group pre- and post-test design. A total of 170 elementary school students aged 9–12 years from Cimahi City were recruited using simple random sampling. The intervention involved the use of the HI Bogi AR-based application for 21 days. The research instrument was an observational questionnaire comprising 13 indicators of toothbrushing skills. Data were analyzed using a paired t-test for normally distributed data and the Wilcoxon signed-rank test for non-normal data. Results: Toothbrushing skills improved significantly following the intervention (Wilcoxon signed-rank test: Z = −15.192, p < 0.001). The mean toothbrushing skill score increased from 4.40 ± 3.77 at baseline to 12.62 ± 0.71 after the intervention, representing an average improvement of 8.22 points. These findings indicate that the HI Bogi AR application substantially improved children’s toothbrushing skills. Conclusion: The HI Bogi application integrated with augmented reality (AR) proved effective in improving proper toothbrushing skills among children aged 9–12 years in Cimahi City. This innovation has the potential to serve as an alternative, promotive, and preventive oral health education tool to support school-based oral health programs.