Particularly in adolescence, fostering adaptive emotion regulation is an important aim in health promotion. Expressive writing in combination with psycho-education on emotion regulation seems especially appropriate to serve this aim. In this study, school classes were randomly assigned either to a prevention (N = 208) or to a non-treatment control group (N = 151). The prevention group showed significant improvements regarding negative affect, grades, and days absent compared to the control-group. A combination of expressive writing with elements of psycho-education of emotion regulation might be an effective preventive tool, as it seems to improve psychosocial adjustment by establishing functional emotion regulation strategies.