Faced with the sudden outbreak of the COVID-19 pandemic, Chinese K-12 schools pivoted to online teaching to "suspend classes without stopping learning" and to ensure continued learning in the first half of 2020. As an emergency measure to combat the pandemic, the implementation of online teaching met a range of challenges. This study randomly distributed approximately 420,000 questionnaires to primary and secondary students, teachers, and administrators across all provinces in China, with the aim of investigating online teaching during the pandemic from the perspectives of teaching organization, policy implementation, and learning experience, as well as comparing the ways urban and rural schools responded to COVID-19 from the perspective of balanced education development. Results show that schools across different regions in the country are equipped with essential facilities for online teaching, guaranteeing the successful rollout of online teaching. It is also found that schools need to enhance their capacity for contextualized decision making and innovation in teaching practice and that additional support should be given to rural schools to improve their access to resources and their online teaching experience. Significant differences between urban and rural schools are found to exist in such areas as students' learning interest and effectiveness, information technology literacy, and psychological well-being. Moreover, there also exists considerable discrepancy in teachers' digital teaching competence between urban and rural schools. We discuss the implications from the findings of this large-scale study and make suggestions for future directions of online teaching development in the digital age. [Translation by Desmond Cheung.]