Background: Approximately one third of California school-age children are overweight or obese. Legislative approaches to assessing obesity have focused on school-based data collection. During 2010-2011, the Chula Vista Elementary School District conducted districtwide surveillance and state-mandated physical fitness testing (PFT) among fifth grade students. We compared height, weight, and body mass index (BMI) to examine measurement differences between the projects. Methods: We assessed demographic characteristics and BMI category frequencies. We used paired t-tests to test continuous variables. ? statistics were used to assess categorical agreement. Results: Of 3549 children assessed, 69% were Hispanic. Fifty-one percent were boys. Mean heights, weights, and BMIs were significantly different for each project (p?<?0.0001). Surveillance height (106.7-165.1?cm) and weight (21.6-90.8?kg) ranges were lesser than PFT ranges (109.2-180.3?cm and 22.7-98.4?kg). The overall BMI category agreement was good (weighted ??=?0.77). Categorical percentage agreement was highest among normal weight children (94.9%) and lowest among underweight children (56.6%). Conclusions: Methodological differences might have resulted in the observed height, weight, and BMI differences. As school-based interventions become common, districts should carefully consider measurement reliability, training, and data-handling protocols to have confidence in their findings.