According to the Council of Europe, educators lack awareness on the topic of digital citizenship education and its importance to educate youngsters to move critically in a highly digitalized world. It is a core component of Digital Citizenship Education (DCE) to promote democratic competences, including critical reflection, the development of social and intercultural competences, critical thinking and media literacy. Bearing this in mind, a Teacher Training Package (TTP) was developed, aiming to promote professional development and qualification of pre- and in-service Foreign Language teachers as well as teacher trainers, as far as DCE is concerned, namely, pedagogical methodologies, practices and resources. Our study focuses on the Free Online Training Course for Self-guided Professional Development (part of the TTP), which directly approaches teachers' professional knowledge. The analysis of the Teaching Units designed by the teachers and of their final course reflections suggest the relevance of the training course for the teachers' professional development. Those who took part in the course highlighted the pertinence of the topic and underlined the relevance of having had contact with theoretical information and resources, which allowed them not only to reflect on their current practices but also to consider ways of introducing DCE in their lessons.