Background: Schools are a channel to better inform, and health educate children and adolescents about the hazards of tobacco smoking increasing their chance of stopping smoking, or even prevent its sporadic or regular use. Objective(s): To assess primary public school children's knowledge regarding smoking, its associated factors, and to evaluate the impact of an educational session about tobacco smoking on the knowledge of school children in Alexandria Governorate, Egypt. Methods: A one- group pretest-posttest design was conducted targeting a total number of 565 primary public-school children by using a pre-designed self-administered questionnaire, as a tool for assessment of their knowledge before and after applying an educational session for them. Results: Current smokers among the participant students accounted for 6.1% (6.2% of girls vs. 5.9% of boys), while 7.1% were ever smokers. Students with good knowledge constituted 9.7%, while those with poor knowledge represented 37.7%. Five items showed less than 50% correct response before the intervention and improved significantly (p = 0.000) after the intervention, namely “Nicotine is the substance that gives the distinctive flavor of cigarettes and is also used as an insecticide", “Cigarettes contain toxic substances such as arsenic and cyanide", “Tobacco kills nearly half of its users", “Drinking waterpipe (Shisha) is less harmful than cigarettes", and “Electronic cigarettes have no harm and help in quitting smoking". Education of the mother (beta = 0.139, p= 0.017), information on packets (beta = 0.135, p = 0.015), having a friend who is smoker (beta = -0.135, p = 0.005), having a working mother (beta = 0.131, p = 0.006), gender (beta = 0.128, p = 0.007), and smoking status (beta = - 0.119, p = 0.012) were the most important predictors of the baseline knowledge score. The total knowledge of the participating students improved significantly after intervention, there was a highly statistically significant difference in the median score before and after the intervention (9 vs. 13, p = 0.000). Conclusion: The lower incidence of smoking among the children having better knowledge combined with the revealed result of the effectiveness of the educational intervention in improving the knowledge of school children especially at that young age mandate the integration of such education among the school curricula.