This research was conducted to determine classroom teachers' positive and negative experiences, opinions, and suggestions regarding online education and mathematics teaching during COVID-19. A phenomenographic research method was used in the study to achieve this aim. The sample group of the study consisted of 14 classroom teachers. This research was conducted online using the semi-constructivist interview technique. In this study, the answers to "How to teach mathematics with online education?", "What are the positive and negative effects of online education on mathematics teaching?" and "What can teachers, students, and parents do with mathematics education in this process?" were sought. It was observed that during the COVID-19 pandemic, classroom teachers entered a new process in online education and mathematics teaching. As a result of the study, it was determined that students had difficulties while studying mathematics. In addition, it was observed that classroom teachers make more effort to teach mathematics in online education than in face-to-face teaching. Classroom teachers also made various suggestions about successful mathematics education with online education to students and parents.