The purpose of this study was to determine the relationship between endurance running performance and aerobic capacity (maximal oxygen uptake: VO₂max, velocity at ventilatory threshold: vVT, running economy: RE) in elementary school boys, in relation to their development and height growth. Ninety-three healthy elementary school boys participated. Endurance running performance was evaluated in terms of running velocity at VO₂max (vVO₂max), which was measured by an incremental running test on a treadmill. VO₂max, vVT and RE were also measured in the same way. It was found that vVO₂max was significantly related to VO₂max, vVT and RE. Chronological age was significantly related to absolute VO₂max (L·min⁻¹), vVT and RE but not relative VO₂max (mL·kg⁻¹·min⁻¹). Among developmental factors, chronological age was significantly related to VO₂max, vVT and RE, but not VO₂max. Therefore, we conclude that the factors contributing to improved endurance performance of elementary school boys are VO₂max, vVT and RE. With regard to development and related height growth, endurance performance could be attributable to vVT and RE (i.e. qualitative changes) rather than VO₂max (i.e. a quantitative change).