The school system has been identified as a uniquely positioned public institution to play a pivotal role in the promotion of youth physical activity (Pate et al., 2006; United States Department of Health & Human Services [USDHHS]/United States Department of Education [USDE], 2000). Within the school day, physical education should engage participants in health enhancing physical activity for a significant portion of the class time (McKenzie & Kahan, 2004; Pate et al., 2006; USDHHS, 2000), concurrently with psychomotor, affective and cognitive domain learning (National Association for Sport & Physical Education, 2004). Adolescents should be active at least 50% of the physical education class time (USDHHS, 2000). The purpose of this research was to advance, through valid and practical measurement, a mechanism for surveillance of the 50% of class time physical activity recommendation. Specifically, the objective was to establish a pedometer steps/min criterion interval that indicates compliance with the 50% of class time recommendation for high school physical education students. Eighty-four male (n=40) and female (n=44) participants (Age: 16.48±1.19 yrs., Stature: 169.43±9.05 cm, Body Mass: 65.32±11.51 kg, BMI: 22.75±3.70 kg/m2) had their physical activity concurrently measured via the Yamax SW-651 pedometer (Yamax Corp., Tokyo, Japan) and the physical activity portion of the computerized System for Observing Fitness Instruction Time (McKenzie, Sallis, & Nadar, 1991; Keating, Kulinna, & Silverman, 1999). Participants were physically active 39.97±16.43% of the class time, and achieved a steps/min (i.e., steps divided by time pedometer was worn, 35.90±3.98 min) value of 67.02±26.83. Physical activity measures were strongly correlated (r=.98, p=.0001). A steps/min value of 83.01 was predicted, via linear regression, as the cut point for 50% of the class time active ( = 1.596[%PA] + 3.212, t = 41.793, p= .0001, SEE = 5.717, SE slope = .038, r2 = .955). Logistic regression (Constant β=-50.178, Steps/min β=.608, p≤.01) indicated that a steps/min interval of 81 to 85 was the best indicator of the 50% physical activity recommendation. Receiver operating-characteristic (ROC) statistics support steps/min as an excellent discriminator between those participants that were compliant and non-compliant with the 50% physical activity recommendation (AUC=.99, SE=.005, p=.0001). In conclusion, pedometer measured physical activity, expressed as steps/min, within high school physical education has demonstrated validity for assessment of the 50% physical activity recommendation; therefore, implementation of pedometry for surveillance of physical education physical activity is warranted.Keyword(s): exercise/fitness/physical activity, measurement/evaluation, research