Standardized testing plays a pivotal role in education. The results of standardized testing are used as performance metrics for students, teachers, and schools. The goal in education is to use performance metrics that are as accurate as possible. There are numerous measurement methods, but a popular choice is Student Growth Percentiles. This study will provide an analysis of Student Growth Percentiles in the Chandler Unified School District, located in Arizona. This study will use the Chandler Unified School District data to calculate standard error measurements and create Student Growth Percentile confidence intervals.