In recent years a public debate has been growing around mobile media and young people, as research has found adverse relationships between the intensive use of smartphones and well-being in this age group. However, there is still a lack of structured interventions targeting teachers and schools on the issue. This paper shows the results of a pre-registered cluster randomised controlled trial evaluating the impact of a media education intervention focusing on screen time management and the conscious use of mobile devices. The impact of a teacher
training course is assessed on their 10th grade students (789 treated, 2572 controls), looking at their smartphone use, digital skills, and subjective well-being. Post-intervention differences, controlling for baseline measures at wave 1, show a moderate but significant decrease in smartphone pervasiveness and problematic use among treated students, with girls displaying greater beneficial effects than boys on withdrawal symptoms. Girls also show an increase in
subjective well-being. No effect is found on the level of digital skills measured with an ad-hoc test. These results highlight that media education interventions focused on screen time management and content-related digital skills can be effectively incorporated into daily teaching and are relevant for students’ well-being. The paper also offers practical indications to develop effective media education interventions in a constant connectivity environment.