This study examined the effect of exercise training on peak VO2 of 26 (12 boys and 14 girls) prepubertal children. Exercise training involved 12 weeks of stationary cycling for 30 min, 3 times · week−1 at 79.3 ± 1.2% (M ± SD) peak heart rate. Nineteen maturity matched controls (10 boys and 9 girls) completed all tests excluding the training. When alterations in habitual physical activity and percent body fat were included as covariates in the analyses, the exercise training did not have a significant effect on peak VO2 for boys or girls. These data may either indicate a maturity related, blunted training response or that prepubertal children require a more intense exercise stimulus.