With the growing trend toward engagement in sedentary behaviors during childhood, a greater understanding of the relationship between cardiorespiratory fitness and cognition during development is of increasing importance. Objective: The aim of this investigation was to assess the extent to which failures in sustained attention may underlie deficits in cognition associated with poorer aerobic fitness. Method: A sample of 62 preadolescent children between the ages of 9 and 10 years were separated into higher- and lower-fit groups according to their cardiorespiratory fitness. Results: Findings indicated that lower-fit children exhibited poorer overall response accuracy during a task requiring aspects of cognitive control relative to their higher-fit counterparts, with a disproportionately greater number of errors of omission, and longer, more frequent sequential errors of omission. Conclusions: These findings suggest that poorer vigilance may contribute to deficits in cognitive control associated with poorer aerobic fitness