PURPOSE: In 2005, the Texas State Legislature passed Senate Bill 42 (SB42), which required public middle school students (grades 6-8) to participate in 30 minutes of daily structured physical activity. The purpose of this study was to assess awareness of and adherence to SB42 in Texas middle schools, and to assess the impact of SB42 on the frequency and quality of structured physical activity. METHODS: Key informant (school principals, physical education [PE] instructors, nurses, or designated personnel) telephone interviews on the implementation of SB42 were conducted from a statewide representative sample of public middle schools (n=112). Direct observation, key informant, and student report of physical activity in PE classes at 17 Texas-Mexico border middle schools assessed the frequency and quality of structured physical activity. RESULTS: State level (94% +/- 4.5%) and border district (94% +/- 13.5%) key informants reported a high level of overall awareness of SB42. Postimplementation of SB42 border districts reported a minimum of 4 days per week of PE instruction and more than 58 minutes per PE class, exceeding the 30-minute minimum of structured physical activity per day or 135 minutes per week as required by SB42 (range: 58.2-61.4 minutes). A significant increase in the number of days of PE class was observed in the border sample between 2004 and 2005 and 2006 and 2008, with eighth grade students reporting an average of 2.0 days and 3.7 days of PE per week, respectively (p < .001). Additionally, border districts met the Healthy People 2010 objective of 50% time in moderate-to-vigorous physical activity (mean 54.9% +/- 5.1%) during PE class. CONCLUSIONS: Implementation of SB42 appears to have impacted the frequency of school PE in Texas and the prevalence of child self-reported physical activity behaviors along the Texas-Mexico border. General awareness of and adherence to SB42 was high in both statewide and among the border districts. Our mixed findings on adherence to specific components of the legislation suggest the need for further investigation of the factors that both facilitate and inhibit local leadership around school policy and the mechanisms to ensure the school policy is being implemented.