Objectives. (1) Determine the predictive value of a school-based test of cardiovascular fitness (CVF) for insulin resistance (IR); (2) compare a "school-based" prediction of IR to a "laboratory-based" prediction, using various measures of fitness and body composition. Methods. Middle school children () performed the Progressive Aerobic Cardiovascular Endurance Run (PACER), a school-based CVF test, and underwent evaluation of maximal oxygen consumption treadmill testing ( max), body composition (percent body fat and BMI z score), and IR (derived homeostasis model assessment index ). Results. PACER showed a strong correlation with max/kg ( = 0.83, ) and with ( = , ). Multivariate regression analysis revealed that a school-based model (using PACER and BMI z score) predicted IR similar to a laboratory-based model (using max/kg of lean body mass and percent body fat). Conclusions. The PACER is a valid school-based test of CVF, is predictive of IR, and has a similar relationship to IR when compared to complex laboratory-based testing. Simple school-based measures of childhood fitness (PACER) and fatness (BMI z score) could be used to identify childhood risk for IR and evaluate interventions.