Objective: This study aimed to evaluate the oral health status of schoolchildren, three years after receiving the routine dental treatment, dental health education and tooth-brushing instruction. Methods: 695 schoolchildren, aged 6-13 years in five schools along Thai-Myanmar border in Kanchanaburi were examined using WHO (1997) oral health examination form in the year 2001 for baseline data. Oral hygiene index was recorded by Greene and Vermillion method. The sealant, filling restoration, scaling and polishing were given. Schoolchildren dental health education and tooth-brushing instruction were performed. After 3 years, 7 parameters of oral health: d, D, dmft, DMFT, debris index (DI), calculus index (CI) and oral hygiene index (OHI) were re-examined to describe data and comparison analysis of all pairs of the 7 parameters (before and after the treatment) was performed. Results: A total number of 408 schoolchildren were completely observed in this 3 year follow-up study. At baseline examination, the average value of age was 8.7 years. While the average values of d, D, dmft, DMFT, were 4.44, 1.62, 4.45 and 1.67, respectively. The percentages of dental caries in the primary and permanent dentition were 83.33% and 63.73%. Most of school children (89.7%) had fair level of oral cleanliness (DI). 88.24% and 71.57% of them had good scores of CI and OHI. All pairs of the 7 parameters (before and after) statistically showed significant differences (p<0.05). The scores of d, dmft, D, DI, and OHI were lower after treatment while those of CI and DMFT were higher. Conclusion: There were some changes in the oral health status of the observed schoolchildren in this study. Their oral hygiene, especially oral cleanliness was better. This study was supported by Mahidol University Research Grant.