There is a lack of valid and reliable low cost observational instruments to measure moderate to vigorous physical activity (MVPA) in school physical education (PE). The participants in this study were third to tenth grade boys and girls from a south Texas school district. The SAM (Simple Activity Measurement) activity levels were compared with heart rates (FIR). It was found that the SAM instrument was feasible and effective at determining MVPA in school-based PE classes as compared to HR monitoring. The results suggest that the SAM is a user-friendly tool that provides an economical and effective tool to measure student school-based PE, MVPA levels. The findings support SAM as an affordable alternative for schools to assess the MVPA levels of students in PE who cannot afford measurement technologies like HR monitoring. The SAM is not limited to students only. SAM can assess PA of adults also. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]