Purpose: To compare students' knowledge, attitudes towards oral health, and plaque scores after oral health education sessions delivered by trained schoolteachers vs the control group. Materials and Methods: The participants, comprising third-grade students in Amphoe Meuang, Nakhonphanom province (N = 435), were randomly divided into an experimental group (n = 216) and a control group (n = 219). Baseline data of the students' oral health knowledge, attitudes, and plaque scores were collected at the beginning of the study. The experimental group was given oral health education sessions by trained schoolteachers using a specifically designed student handbook, while the control group did not receive extra oral health education other than the national curriculum. The immediate post-test knowledge was evaluated after each session, and plaque scores were determined after the brushing session. After the oral health education programme ended, the experimental and control groups performed a monthly toothbrushing activity for 2 months. Final assessment of the students' knowledge, attitudes, and plaque score was done at the 3-month follow-up. Results: The experimental group's oral health knowledge statistically significantly improved immediately after each session and was still statistically significant during the following three months. This improvement was also statistically significantly higher compared with the control group. The attitudes towards oral health care, foods related to caries, and dental visit improved. The plaque score of the experimental group was statistically significantly lower immediately post-brushing, but was not statistically significantly different at the 3-month follow-up compared with baseline. Conclusion: The children receiving oral health education provided by trained schoolteachers had statistically significantly greater oral health knowledge and more positive attitudes towards oral health than the children who had not received the programme. No statistically significant differences in plaque scores were found after 3 months. Keywords: attitude, knowledge, oral health education, primary schools, schoolteacher