Objective: The aim of the study was to compare the change in energy balance-related behaviors from 2000-2002 to 2004-2005 between 2 Texas regions with distinct patterns in obesity prevalence (decrease in the El Paso region [EP] and leveling off in the Rio Grande Valley region [RGV]) and to determine the role of the behaviors in the difference in obesity prevalence between the regions. Design: Cross-sectional measurements of the School Physical Activity and Nutrition Study. Setting: Elementary schools. Participants: 3,949 children (9-10 years). Variables Measured: Body mass index (objectively measured) and behaviors (self-assessed). Analysis: Probability and post-stratification weighting procedures and mediation analysis. Results: Compared to students in the RGV, students in the EP experienced a smaller decrease in sports team participation, an increase in regular meal consumption, and an increase in the frequency of milk/yogurt, cereal, sweet snacks, and frozen dessert consumption between measurement periods. Prevalence of frequent television viewing was lower in the EP. The lower body mass index in the EP was associated with regular meal consumption, and higher milk/yogurt and sweet snack consumption. Conclusions and Implications: Improvement of physical activity, sedentary behaviors, and healthful diet, but not unhealthful diet like sweet snack consumption, seem to be related to the decrease in obesity in the EP. (Contains 2 figures and 2 tables.)