The COVID-19 pandemic has been an unprecedented disruption in students' academic development. Using reading test scores from 5 million U.S. students in grades 3-8, we tracked changes in achievement across the first two years of the pandemic. Average fall 2021 reading test scores in grades 3-8 were 0.09 to 0.17 standard deviations lower relative to same-grade peers in fall 2019, with the largest impacts in grades 3-5. Students of color attending high-poverty elementary schools saw the largest test score declines in reading. Our results suggest that many upper elementary students are at-risk for reading difficulties and will need targeted supports to build and strengthen foundational reading skills.