FITNESSGRAM is the most widely used youth fitness assessment and reporting tool in school physical education programs. It has been adopted by thousands of schools in the United States and is required as a mandated statewide fitness assessment tool in several states. While developed primarily for educational applications, FITNESSGRAM also has utility for research and public health applications. This dissertation summarizes FITNESSGRAM outcomes from two large applications to advance research on youth fitness research and practice. The first application, Texas Youth Fitness Study, involved the evaluation of statewide data collected in the state of Texas as part of mandated school fitness testing. Approximately 2 to 3 million students were tested with FITNESSGRAM each year across Texas. Study 1 revealed significant school- and county-level correlates explaining the variability in weight status from Texas youth. Study 2 examined the longitudinal weight status change in children and adolescents in Texas. Positive shifts in weight status were found among most age groups in Texas youth between 2011 and 2014. The second application, NFL PLAY 60 FITNESSGRAM Partnership Project, involved over 1,000 schools across the United States where millions of students participated. Study 3 used individual student FITNESSGRAM data collected over 4 years of the project to examine the longitudinal effects of NFL PLAY 60 programming on youth aerobic capacity and body mass index. The results revealed significant improvements in aerobic capacity and body mass index profiles in schools that implemented the school-based health promotion programs. This dissertation work provides novel findings about youth fitness profiles and demonstrates the utility of evaluating the impact of school programming using systematic evaluation of FITNESSGRAM data.