Introduction The aim of our study was to investigate the effect of an Oral Health Promoting School (OHPS) model on children's oral health in Iran. Methods This interventional quasi-experimental study was conducted in the academic year 2019–20 among 354 primary school students and their parents. A questionnaire including 17 questions was distributed among children before and 5 months after the program (The ranges of possible scores = 0–17). Training workshops for the parents based on the theoretical domains framework were designed. Using educational sessions, pamphlets, tooth brushing dairies, assignments to do at home, educational videos and messages as reminders in social networks, parents were educated about dental caries, its risk factors and prevention principles. Best recommended oral health behaviors including tooth brushing and the use of fluoridated tooth paste were also educated. A questionnaire consisting of 18 knowledge (The ranges of possible scores = 0–18), 13 attitude and 10 practice questions were distributed among parents before and after the workshops. The data were fed into SPSS and analyzed by descriptive and analytic statistics such as T-test, ANOVA and Correlation Coefficients (α = 0.05). Results The mean pre-test knowledge (7.8 ± 1.7) was increased significantly in three schools after program, p < 0.001. In the post-test, girls gained significantly higher scores (9.61 ± 1.98 vs. 9.06 ± 1.4, p = 0.025). Among 147 parents, the mean knowledge was raised from 12.3 ± 3.1 (5–18) to 15 ± 3.03 (6–18), p < 0.001. Knowledge score of the parents attending both sessions was higher. Practice of the parents regarding the use of fluoridated tooth-paste was significantly improved (p < 0.001). Also, their attitude toward the ability of children to take care of their teeth was improved (p = 0.029). Based on the self-report of parents, 71.4% (n = 47) of mothers and 45.6% (n = 67) of their children used to brush once or two times daily and there was a correlation between their behaviors (p < 0.001, Spearman Correlation Coefficient = 0.4). Conclusion It seems that the education provided in OHPS had positive effects on increasing students' awareness and to some extent, the knowledge, attitude and practice of the parents.