At the beginning of 2020, teachers had an unexpected experience. The COVID-19 pandemic forced teachers to change their way of teaching from face-to-face to virtual. The purpose of this study was to explore the challenges faced, and the strategies used for online teaching by teachers during the transition from face-to-face to virtual classes. Moreover, interpret if teachers were prepared to start virtual classes. Using a qualitative approach, a questionnaire and an interview were applied. The sample consisted of 6 volunteer teachers from different subjects for the interview and 40 teachers for the questionnaire. The challenges revealed by the interviewees were Poor connection, Lack of student resources, and Mastery of digital tools. Regarding the strategies, Role-Playing, Presentation, Repetition, and Learning based on problem-solving were used. Finally, the results of the questionnaire showed that the majority of the teachers were prepared to start virtual classes. Considering the reviews of other similar studies and the results in this study, certain implications could be mentioned. Although the teachers were able to overcome the challenge of virtual classes, it was evident how complex the transition was. It is necessary to keep in mind that virtuality is here to stay and the online classroom will continue to be part of the teaching and learning process. Therefore, training for teachers should be included not only on the use of technology but also on strategies for effective online teaching.