Although numerous media literacy training sessions on internet safety for children and adolescents have been conducted, their number contrasts sharply with the few systematic studies on their effectiveness. In this study, we describe the evaluation of nationwide-implemented training sessions on internet safety in Luxembourg, which included perceptions of learning outcomes and evaluations of implementation and effectiveness. Training data from 2011 to 2018 were analyzed, including 28,060 students and 5,031 teachers. Students reported pronounced learning effects, especially for younger students and for repeated training participation. Teachers greatly appreciated the implementation and effectiveness, which generally increased over the years. The perceived effectiveness of the training was significantly related to teachers’ planning to cover internet safety topics in future lessons. The present study shows that carefully planned and continuously evaluated training sessions on internet safety successfully support children’s understanding and teachers’ willingness to implement internet safety in their curriculum.