Being overweight is a major risk factor for development of lifestyle-related diseases, and the sheer volume of current evidence that childhood obesity persists into adolescence and adulthood suggests the importance of rectifying obesity in childhood. The present study followed up children in the 1st to 6th grades of elementary school to examine whether being overweight was a continuous trend. In addition, increases and decreases in the adiposity of the students were examined in order to clarify fluctuations in their physical build. The subjects of the study were 3991 students (2046 boys and 1945 girls) attending all 68 schools in city U who were tracked for 6 years. The students were divided into 10th percentiles based on their degree of overweight. Using the median 45-55th percentile as a reference group, univariate logistic analysis was used to calculate the odds ratio of students who were overweight in the 1st grade remaining so in the 6th grade. It became clear that students in the 85th percentile or higher in first grade were 39.8 times more likely for boys and 21.9 times more likely for girls to be overweight in the 6th grade than 1st grade students in the reference group. Boys and girls who were markedly overweight in the 1st grade continued to demonstrate high degrees of obesity in the 6th grade. About 80% of both boys and girls who were overweight in the 1st grade of elementary school continued to be overweight in the 6th grade. Based on the above findings, it is clear that the degree of overweight in the 1st grade of elementary school has a strong influence on the corresponding degree in the 2nd grade and thereafter, thus suggesting the importance of preventing overweight developing upon entry to elementary school.