This research was designed to test the effectiveness of a school network for childhood obesity prevention (SNOCOP) in primary schools; a program that aimed to improve student behavior in terms of knowledge, attitude, intention towards obesity prevention, and their food consumption behavior. A quasi-experimental pretest-posttest time series study was conducted. By 2-stage stratified sampling selection 180 students from 6 schools were assigned to the intervention group and 195 students from 6 schools to the control group at Saraburi Province, Thailand in 2006- 2007. In addition, thirty-one participants being school administrators, teachers, parents, and community members from six schools formed the social network initiating the intervention. The schoolchildren in the intervention group improved their eating behavior, knowledge, attitude, intention towards obesity preventive behavior. The six schools of the intervention group changed school policies and school activities aiming to reduce the proportion of obesity among their student. No such activities could be observed in the control group. These findings suggest that the School-Social Network of Childhood Obesity Prevention program is an effective means to prevent childhood obesity.