Using the balancing task in a sitting position on a Swiss ball in the educational domain of physical fitness for the middle grades of elementary school, the present study attempted to clarify the characteristics of the action of postural maintenance.The number of instances of taking a seat, duration of postural maintenance, and postural maintenance were measured in 45 third-grade school children. These measurements were used to calculate the horizontal distances pertaining to postural maintenance (Center-Toes-Distance: CTD; Center-Ischium-Distance: CID; Center-Ear-Distance: CED), from the center of the Swiss ball to 3 points of the body (toes, ischium, and external auditory meatus). Based on these measurements, the overall characteristics of the action of postural maintenance were noted, and the characteristics of the children with low task achievement (low group: 10 children) and those with high task achievement (high group: 14 children) were compared.With regard to postural maintenance, a significant negative correlation was established between CTD and CED. This indicated that, in the balancing task, the children's postural maintenance was characterized by linking the flexion and extension movements of the lower limbs and the forward and backward tilting movements of the upper body with the occupied surface of the Swiss ball as the base point. Furthermore, the mean values of CTD, CID, and CED in the low group were 57.3±15.4 cm, 1.7±5.1 cm, and -11.3±6.2 cm, respectively, indicating that the group's sitting posture was characterized by leaning forward from the center of the Swiss ball. By contrast, the corresponding values for the high group were 42.9±20.8 cm, -3.4±2.3 cm, and -3.9±3.6 cm, respectively. Furthermore, a comparison of the mean values between the groups showed a significant difference in CID, suggesting the necessity of sitting posterior to the center of the Swiss ball in order to maintain a stable posture.The aforementioned findings revealed the characteristics of the low and high groups as well as the overall characteristics of postural maintenance in the balancing task in a sitting position. Moreover, the findings provided a perspective for examining the learning content and stages based on the actual conditions of children, in terms of exercise guidance with the use of a Swiss ball. These findings indicate that exercises involving riding on equipment such as the Swiss ball can be used to teach children about movements by which they can adapt to an unstable environment.