Iodine Deficiency Disorders (IDD) is health problem of Thailand which affected physical and brain development. Primary school students, especially among those in Roi-Ed province are the risk group of IDD. The main objective of this quasi-experimental research was to assess the effectiveness of health - promotion student-leaders on preventing iodine deficiency disorders among primary school students in Nongpuak District, Roi-ed Province. PRECEDE Framework and Cone of Experience were modified for health education program design. The subjects were 129, grade 4-6 primary school students. Sixty seven students from Ban loaphone - ngam School and sixty - two students from Nongkoonvitayakarn School were assigned to be the experimental group and comparison group respectively. The experimental group was scheduled to participate in program designed under health - promotion student - leaders activities. The study was devided into three phases, Pretest,Postest and 2-week follow - up. Frequency distribution,percentage, arithemetic mean,standard deviation,t-test and Pearsons product moment correlation coefficient were used to analyse the data. According to the post-test, and 2 - week follow up phase,the findings showed that the experimental group gained knowledge about IDD, positive attitude towards drinking iodate water more significantly than prior to participating the program. In addition, the experimental group also believed in IDD affecting physical and brain development more positively and significantly than prior to participating student leaders activities Eighty - two percent of students in experimental group were drinking water with iodine solution. There were significant correlation between knowledge belief and drinking of water with iodine solution. Regarding the research findings, health personnel are encouraged to more fully apply of the health-promotion student- leaders strategies to cope Iodine Deficiency Disorders and other diseases in order to attain health behavior change among the target population.