This research article from the Center for Education Policy Research at Harvard University and the Education Opportunity Project at Stanford University analyzes data from approximately 7,800 school districts to describe variation in pandemic-related learning losses among communities and student subgroups. The authors sought to understand mechanisms that led to learning losses and explore how historical data from those districts can inform our expectations for how quickly districts will rebound from such losses. They show that learning losses during the pandemic were large and highly variable among communities. Similar to previous research, the authors find that losses were larger in lower-income and minority districts and in districts that remained remote or hybrid for longer periods during the 2020–21 school year. Among districts, the mathematics learning loss per week of remote or hybrid instruction was larger in high-minority and high-poverty districts. Within districts, however, White students and non–economically disadvantaged students lost about the same amount of ground as Black, Hispanic, and economically disadvantaged students.