The Government Accountability Office (GAO) was asked to examine the prevalence and growth of segregation in K-12 public schools. This report examined the extent of (1) racial, ethnic, and economic divisions in K-12 public schools; and (2) district secession and any resulting student demographic shifts. To determine the extent of divisions along racial, ethnic, and economic lines in schools, GAO analyzed demographic data from Education's Common Core of Data by school type, region, and community type, covering school years 2014-15 to 2020-21, the most recent available data since GAO last reported on this topic in 2016. To identify the number and location of districts that seceded from school year 2009-10 through 2019-20, GAO analyzed and compared school district data from the Common Core of Data for the new and remaining districts in the year after secession to identify and describe any differences in demographic and socioeconomic characteristics. Findings showed that as the K-12 public school student population grows significantly more diverse, schools remain divided along racial, ethnic, and economic lines throughout the U.S. These divisions span school types, regions, and community types (urban, suburban, and rural). Because diversity within a school is generally linked to the racial/ethnic composition of the district, school district boundaries can contribute to continued divisions along racial/ethnic lines. GAO's analysis of 10 years of Education data shows that district secession--a process by which schools sever governance ties from an existing district to form a new district--generally resulted in shifts in racial/ethnic composition and wealth.