This report is part of a series that aims to provide a definitive account of the best available evidence on how the COVID-19 pandemic has affected America's students. The series is part of a broader effort, the Evidence Project, which brings together researchers and policymakers to advance solutions-oriented analysis of the K-12 response to the COVID-19 pandemic. Determining how the pandemic and associated disruptions to schooling have affected the development of students' foundational academic skills is critical. Yet gauging the academic impacts of the pandemic is hard: its disruptions to schooling also disrupted the assessment systems used to monitor students' progress. Annual state tests were cancelled in spring 2020 in all states. Even where interim assessments continued, many students did not participate--and those who did not participate are likely to be the same students who experienced the greatest impact from the pandemic. Finally, changes in the mode of administration (e.g., more students taking tests from their homes) raise questions about the validity of the data and their comparability to prior years. Despite these challenges, a body of evidence is emerging that sheds partial light on what has happened to student achievement overall and for demographic subgroups. In June 2021, the Center on Reinventing Public Education (CRPE) gathered a panel of 10 experts in education policy and assessment to review the available evidence on the pandemic's impact on students' academic skills. This report summarizes the evidence on how the pandemic and the converging social events of 2020 and 2021 affected K-12 students' academic progress.