The research featured in this paper is part of the CORE-PACE Research Partnership, which is focused on producing research that informs continuous improvement in the CORE districts as well as policy and practice in California and beyond. Since spring 2020, the COVID-19 pandemic has been abruptly interrupting regular instruction in almost all schools in the U.S. One year later, policymakers, district administrators, and educators are still balancing the benefits and risks of returning K-12 students to fully in-person school. Many are concerned about the pandemic's disruption to students' academic progress. In California, educators have been focused equally on students' mental and emotional health, social relationships, and learning environment, given that many students have been learning remotely since the onset of the pandemic. Anticipating the need for schools and districts to understand their students' social-emotional well-being, the CORE Districts in California developed survey instruments to collect such information in the 2020-21 school year. The surveys were administered remotely, as all participating districts offered distance-only instruction. This report draws on data from the "Student well-being and learning conditions diagnostic survey" taken by 32,000 students in Grades 4-12 from three districts at the beginning of the 2020-21 school year. The results from 15,000 students who also responded to the "Comprehensive interim survey" a few months later are also highlighted. This report brings data to bear on the areas of student well-being that are most relevant at each developmental stage, so that all education stakeholders are able to focus their efforts on meeting the most pressing needs of each group of students.