Prior to adolescence, children exhibit lower cognitive performance when compared with young adults, likely due to the underdeveloped neurological structures that underlie such processes (Diamond & Taylor, 1996; Travis, 1998). However, regular physical activity has been shown to have a significant positive impact on cognitive processing during development, and both physiological mechanisms and learning have been suggested as potential causes (Sibley & Etnier, 2003). Regular physical activity and increased fitness have been related to better performance on executive control tasks in adults (Hillman et al., 2004; Kramer et al., 1999). Executive control refers to a subset of processes involved in the intentional component of environmental interaction and includes response selection and inhibition, action monitoring, mental flexibility, and other complex cognitive processes. The Stroop task is one assessment of cognitive processing that measures aspects of executive control related to attentional selection and inhibition by varying the degree of cognitive interference between tasks (word, color, color-word). The present study investigated performance on the Stroop task in 64 (37 males) healthy preadolescent children (M = 9.4 years). Physical fitness was measured using the Fitnessgram, a valid and reliable field assessment of physical fitness in participants from age five through adulthood. Children completed multiple aspects of the Fitnessgram, including aerobic capacity (i.e., the PACER --Progressive Aerobic Cardiovascular Endurance Run), muscle fitness (i.e., push-ups and curl ups), flexibility fitness (i.e., sit and reach test), and body composition through height and weight measures that are converted to a body mass index (BMI) score. Partial correlation analyses were conducted between the three Stroop conditions and the Fitnessgram subtests, controlling for age, sex, and IQ. Results indicated a significant positive relationship for aerobic fitness and the color and word Stroop tasks, conditions which require lesser amounts of executive control. However, a significant relationship was not observed between fitness and the color-word condition of the Stroop task, which requires greater amounts of executive control. These findings suggest fitness positively influences tasks requiring lesser amounts of attentional selection and inhibition (i.e., reading ability), but may not benefit tasks requiring greater amounts of this particular aspect of executive control in preadolescent children. These results will be discussed in terms of neurobiological development.Keyword(s): elementary education, exercise/fitness, research