Though once a leader in school integration, Massachusetts has regressed over the last two decades as its students of color have experienced intensifying school segregation. This report investigates trends in school segregation in Massachusetts by examining concentration, exposure, and evenness measures by both race and class. First, the report provides a brief overview of the history of school desegregation in the state and in several prominent school districts. Then is summarized several decades of social science research highlighting the harms of segregation and the benefits of diverse learning environments. The next section describes the report's data and methods. Examined are enrollment patterns and several measures of desegregation at the state level. After exploring trends at the state level, next explored are the Boston and Springfield metropolitan areas with similar measures provided of segregation for each metro area; this section will also discuss the degree and type of racial transition occurring in the ten largest districts in each metro. The report concludes with a discussion of findings and multiple recommendations for those who seek to address segregation in Massachusetts schools. Fact sheets documenting segregation trends in four of Massachusetts's metro areas also accompany this report. The following are appended: (1) Additional Data Tables; and (2) Data Sources and Methodology. [The report was written with John Kucsera, Genevieve Siegel-Hawley, and Gary Orfield. This is the third of thirteen in a series of special reports on public school segregation in Eastern states. These studies explore trends in enrollment and school segregation patterns from 1989 to 2010 at the state and regional levels, including various metro areas for each state.]