The OMNI Perceived Exertion Scale was developed to help children report perceptive effort during exercise. To date, no studies have validated the OMNI scale in an age-diverse sample of youth using lifestyle activities. PURPOSE: To evaluate the concurrent validity of the OMNI Perceived Exertion Scale (walk/run format) in four age groups of children performing a variety of lifestyle activities. METHODS: 206 (105 boys, 101 girls) participants between the ages of 6 and 16 were stratified into four age groups: 6-8 years (n = 42, mean age = 7.2 ± 0.71 y), 9-10 years (n = 46, mean age = 9.5 ± 0.51 y), 11-12 years (n = 47, mean age = 11.5 ± 0.51 y) and 13+ years (n = 71, mean age = 13.9 ± 1.0 y). All participants completed 11 trials including, handwriting, computer game, sweeping, throw and catch, laundry task, step aerobics, basketball, comfortable walk over ground, brisk walk over ground, brisk walk treadmill, and running over ground. Each trial lasted 5 min. During each trial, heart rate and VO2 were continuously measured via a portable indirect calorimetry. Immediately after each trial, participants reported their perceived effort by selecting a number from 0 to 10 from the OMNI scale. Concurrent validity was assessed by calculating within-subject correlation between OMNI rating and three physiological indices (HR, VO2, and METs). For each age group, within-subject correlations were averaged using the fisher-z transformation. RESULTS: The correlation between OMNI ratings and the physiological indices increased with age in a dose-response manner. The average correlation between OMNI ratings and VO2 was 0.67, 0.77, 0.85 and 0.87 for the 6-8, 9-10, 11-12 and 13+ y age groups, respectively. The average correlation between OMNI ratings and HR was 0.67 0.77, 0.85 and 0.87 for the 6-8, 9-10, 11-12 and 13+ y age groups, respectively. The average correlation between OMNI ratings and METs was 0.65, 0.77, 0.84 and 0.85 for the 6-8, 9-10, 11-12 and 13+ y age groups, respectively. CONCLUSIONS: The OMNI Perceived Exertion Scale is a useful measure of effort perception among children; however, the relative validity of the scale appears to be strongly age-dependent. The lower validity coefficients observed among 6- to 8-year-olds suggest the scale should be used with caution in children under the age of 9. Funded by NICHD (HD055400-02)