The Every Student Succeeds Act (ESSA) devolves many decisions to states about how to design their accountability system and the measures to use in these systems in order to meet new goals of college and career readiness. Because few states presently have adequate measures for the new goals, they will need to develop the measures along with accountability structures. ESSA includes a provision that would allow district waivers to their state’s programs. States can use such waivers to make use of particularly high-capacity districts’ ability to innovate and test new approaches. The CORE districts in California serve as a model for the potential for waivers to benefit their state as well as other states. These districts received the only district-level waivers from No Child Left Behind and have designed a new accountability system that incorporates a wide range of measures that could also be used under ESSA. In collaboration with Policy Analysis for California Education (PACE), CORE has produced a series of reports about their experiences with the new measures that are important with respect to future state and federal policy. Among the significant findings are the large impact on which schools are identified as underperforming that follows from decisions about the minimum number of students that must be included to calculate and report on the academic outcomes of subgroups of students, such as African-Americans. In a similar vein is the finding that only 13 percent of schools that are identified as low-performing based on end-of-year test scores in a given year are likewise identified as low-performing when the measure is growth of test scores from the end of one year to the end of the next. Not all states will need district waivers or have districts that could provide the kind of insights that the CORE districts have been able to. But states with both the need and such districts could use the waiver provision to help them to develop and refine an accountability system under ESSA.