To examine which aspects of children's fitness assessment are associated with their performance on four different academic areas. FITNESSGRAM measures aerobic capacity, abdominal strength, upper body strength/endurance, flexibility, and trunk lift. Gender and a socio-economic status proxy were compared with mean group performance scores across four subscales: mathematics, reading/language arts, science, and social studies of a statewide standardized academic performance test on a sample of 968 5th grade students (50.7% male; mean age=10.6 years). Achievement test scores were significantly better for children who were in the Healthy Fitness Zone (HFZ) for aerobic capacity and abdominal strength tests when compared to children who were unable to achieve the healthy zone. Children in the HFZ for upper body strength performed significantly better in math. Children in the HFZ for flexibility performed significantly better in math and science. No differences were found in academic performance when children in the HFZ for trunk lift were compared to children not in the healthy zone. When all FITNESSGRAM measures were used in a full factorial ANOVA with Body Mass Index (BMI), gender and meal program (a proxy variable for socioeconomic status) as covariates, aerobic capacity was found to be the only fitness variable consistently appearing as important. It was always significant as a main effect variable while no other main effect fitness variable achieved significance for any WEST-EST subject. Two-way, three-way, and four-way interactions always included aerobic fitness and no other fitness measure was universal in these interactions. Whereas, aerobic fitness appears universally important in academic success, additional mechanisms may be at work due to the several interactions that achieved significance. The interactions may be an indication of the importance of overall fitness in addition to aerobic fitness. These findings support the development and implementation of childhood cardiovascular risk surveillance programs that not only evaluate children's overweight risks but also their fitness. Increased focus on ways to improve children's fitness levels may create the need to reevaluate current policy recommendations for children's physical education.