The COVID-19 pandemic disrupted learning for millions of students, educators, and families who had to navigate modified in-person and virtual schooling, often in difficult circumstances. The pandemic's effects continue to reverberate across the nation and produce challenges for schools that will likely be felt for years to come. In many respects, the 2020-21 school year offered useful insights that may help schools, educators, and parents in the future. The CARES Act includes a provision for the Government Accountability Office (GAO) to report on its ongoing COVID-19 monitoring and oversight efforts. GAO also conducted this work in response to a provision in the conference report accompanying the National Defense Authorization Act of Fiscal Year 2021. This report, which is the first in a series of reports, examines: (1) obstacles to learning during school year 2020-21; and (2) strategies to mitigate learning loss. GAO examines these topics overall, by grade level, and by instructional model (in-person, virtual, or hybrid). To address these objectives, GAO contracted with Gallup to: (1) conduct a nationally representative survey of K-12 public school teachers; and (2) arrange virtual discussion groups with teachers, principals, and parents of K-12 students. GAO also held two additional discussion groups, one with teachers and one with parents of students in Department of Defense Education Activity schools. GAO analyzed the resulting survey data and discussion group responses.