Previous research has established valid models for determining the energy cost of walking and running, but there are no appropriate criterion standards for a walking test of aerobic fitness for low-fit children that is consistent with ACSM guidelines. Current recommendations prescribe an intensity of at least 50%VO2max. PURPOSE: The purpose of this study was to develop a generalized model for determining the energy cost of walking and develop standards for a 30-minute walking test that might be appropriate for lower-fit children and adolescents to achieve 50% to 60%VO2max. METHODS: Subjects were 101 boy and 79 girl volunteers, ages 9–18 years. Each subject performed a submaximal treadmill exercise test at randomly selected walking and running speeds from 2–8 mph. VO2 was measured by open-circuit spirometry. The sample was randomly divided into a derivation sample of 90 subjects, and a cross-validation sample of 90 subjects. Multiple regression was used to develop models for estimating VO2 (ml.kg-1.min-1) in the derivation sample. RESULTS: The relationship between running speed and VO2 was linear, and the relationship between walking speed and VO2 was curvilinear. The derived equation is: VO2 (ml.kg-1.min-1) = 6.54 + 6.69(mph) - 5.78(mph x walk=1,run=0) + 1.23(mph x walk=1,run=0)2, R2 = .87, SEE = 4.0 ml.kg-1.min-1. Cross-validation revealed very little shrinkage in the derived model (R2 = .86, Error = 4.1 ml.kg-1.min-1). CONCLUSION: Using the derived model, predicted values of 50% to 60%VO2max for children and adolescents whose VO2max values are as low as 12 ml.kg-1.min-1 requires walking speeds between 2.0 and 2.15 mph. Consequently, a 30-minute walk at this relative intensity would require a distance of 1.0 to 1.1 miles. Predicted values of 50% to 60%VO2max for children and adolescents whose VO2max values are 39 ml.kg-1.min-1 requires walking speeds between 3.6 and 3.9 mph. Consequently, a 30-minute walk at this relative intensity would require a distance of 1.8 to 1.95 miles. These data demonstrate that the minimum ACSM requirements for intensity of aerobic exercise can be achieved by a 30-minute walking test of aerobic fitness in children and adolescents.