Online education for higher education has been well-researched. However, the same cannot be said for primary and secondary school education. Using data from two large-scale exams of representative Chinese primary and secondary schools pre- and post-COVID-19 pandemic, this study analyzed the difference in students' performance pre-pandemic, which used face-to-face teaching, and post-pandemic, which used online teaching. Primary results indicate that the performance of primary and secondary students before the pandemic was significantly better than after the pandemic. Secondary results showed that many previously high-scoring students were now scoring closer to the mean. Further, the scores of girls had changed more significantly than those of boys. Online teaching had a negative effect in rural than in urban areas; the preexisting gap between rural and urban students had widened after online teaching. Based on these results, improvements can be made on the online education system, technical support, and teachers.