For the past quarter century, federal law has required states to measure school performance, identify the lowest performing schools, and provide support to identified schools. Earlier accountability systems were criticized for overemphasizing student achievement in reading and mathematics, excluding nonacademic features of school performance, and relying on measures closely associated with student characteristics. However, the Every Student Succeeds Act (ESSA) of 2015 ushered in a new era of accountability, enabling states to design complex systems with multiple measures, with the intention of providing a more holistic picture of a school's overall performance. Based on evaluations of school performance, states are required to identify the lowest performing 5% of Title I schools for comprehensive support and improvement (CSI). This report examines how design choices regarding the measures included in Florida's ESSA accountability system and the method for aggregating those measures affect which schools are identified as CSI. Drawing on administrative data from the 2017-18 and 2018-19 school years, several analyses were conducted examining how many measures each school was rated on and which measures were most often missing, correlation among measures and between measures and student demographics, year-to-year correlations of measures, and simulations designed to evaluate the influence of specific measures on CSI identification.