This study investigated the effectiveness of an intervention (a spine mat) by measuring trunk inclination angle (TIA) and the center of pressure (COP) location while standing. [Participants and Methods] The study participants were 83 elementary school students. Their TIA and the COP location in the upright position were measured before and after the spine mat intervention. [Results] Comparison of TIA showed that the degree of anteversion was significantly reduced in boys (3.04 ± 3.8°) after the intervention as compared to before the intervention (4.34 ± 3.7°). In contrast, there was no significant difference in the TIA in girls. No significant change was observed in the COP location after the intervention in either boys or girls. [Conclusion] The results of this study show that the immediate effect of spine mat intervention on TIA was that only boys showed a decrease in TIA. There was no change in COP location in either boys or girls after the intervention.