The outbreak of COVID-19 pandemic in March 2020 influenced all aspects of school life. Teaching and learning moved only online, with different software solutions emerging for teachers to make the most of them. These educational platforms provided more than just a traditional teaching which is focused on the transmission and access to information. Their added value is in a student-centred approach which promotes diverse competencies as regarded to be 21st century skills. This study focused on promoting 21st century digital skills using educational platforms in the times of COVID-19 during school lockdowns. It examined teachers' responses about the extent to which this promotion was attained during their online teaching using these technologies. A sample of 667 schoolteachers from Serbia was used and relevant data were collected using an online questionnaire. The analysis showed there were significant differences between these medians of promotion of digital skills for different groups of teachers favouring certain groups. These differences could be explained by the fact that teachers in those favoured groups were more experienced in using educational platforms and arranged teamwork within them more often. Additional analysis showed that experience and teamwork were related and that they jointly contributed to digital skills promotion. Suggestions for practice and research are included.