COVID-19 shuttered schools across the United States, upending traditional approaches to education. We examine teachers' experiences during emergency remote teaching in the spring of 2020 using responses to a working conditions survey from a sample of 7,841 teachers across 206 schools and 9 states. Teachers reported a range of challenges related to engaging students in remote learning and balancing their professional and personal responsibilities. Teachers in high-poverty and majority Black schools perceived these challenges to be the most severe, suggesting the pandemic further increased existing educational inequities. Using data from both pre-post and retrospective surveys, we find that the pandemic and pivot to emergency remote teaching resulted in a sudden, large drop in teachers' sense of success. We also demonstrate how supportive working conditions in schools played a critical role in helping teachers to sustain their sense of success. Teachers were less likely to experience declines in their sense of success when they worked in schools with strong communication, targeted training, meaningful collaboration, fair expectations, and authentic recognition during the pandemic.