Wastes crisis is a major problem in the world and an important cause of global warming. Thailand's solid waste management system is inadequate, resulting in accumulated waste. The amount of solid waste tends to increase steadily that caused by human. Management of solid waste problems should be initiated from providing knowledge and understanding of solid waste management and cultivating good consciousness in waste separation, which could reduce waste from the origin. The purposes of this research were 1) to assess the knowledge and understanding of garbage management of students at Wat Samet Nuea school before and after the training 2) to evaluate the results of waste separation before disposal before and after the training 3) to measure opinions of students for the waste management training. The population used was 200 students of Wat Samet Nuea school. The sample was a purposive selection method using 140 students in primary school (P4-6) and junior high school (S1-3) of the academic year 2018. The tools used a set of colored bins (green, blue and yellow), a daily garbage disposal record form, a test of knowledge and understanding of waste management and an assessment form of students’opinions on waste management training. The results presented that before the training, students correctly and incorrectly put waste into the bins about 52.35% and 47.65%, respectively. Students littered waste into the general bin, recycling bin and wet bin 49.94%,35.23% and 26.05 %, respectively. Assessment results of knowledge of waste management of students before and after the training showed that the average scored before and after the training of P4-6 students was 8.64 (S.D.=1.85) and 15.71 (SD=1.51), respectively
(p< 0.01). The average scored before and after the training of S1-3 students was 8.87 (S.D.=1.69) and 16.24 (S.D.=1.35), respectively (p<0.01.). After the training, students correctly and incorrectly littered waste into the bins about 80.15% and 19.85%, respectively. Students littered waste into the recycling bin general bin and wet bin about 85.63%, 79.94% and 72.89%, respectively. Level of opinions of students on waste management training was high (x̅=4.40). Therefore, educating and understanding the correct waste separation at the origin could reduce waste disposal problems in the future. It also cultivates the right attitude in waste management among students.