This research aimed to develop a green school training manual for high school students in Pracharat Wittaya Serm School with an efficiency index at a rate of 80/80. The scores of knowledge, attitudes, and participation of the research participants gauged before and after the training were compared. The simple random sampling method was used to recruit a group of 54 student samples from Pracharat Wittayaserm School in the first semester of the academic year 2021. The research instruments consisted of The Green School Training Manual, The Knowledge Testing Form, The Attitude Testing Form, and The Participation Testing Form. The statistics used in the data analysis were frequency, Percentage, mean, standard deviation, and paired t-test. It was found that the efficiency of the training manual was 80.45/82.60, and the efficiency Index (E.I.) was 0.5840. These statistics indicate that the students had a 58.40 percent of knowledge progression. It was also observed that the average post-test scores of knowledge, skills, and environmental management participation were higher than the pre-tests scores with the significance at the level of 0.05.