Education on sleep hygiene improves sleep knowledge. However, the literature shows that improvements in adolescents' sleep hygiene behaviour are less convincing. We developed an educational intervention for 6 th graders based on self-determination theory and evaluated this program in a pre-post-design with a control group. Pre-test was one week before the intervention, POST1 was directly afterwards, POST2 with a delay of one week, and POST3 after six weeks. Morningness was positively correlated with good sleep practice. The intervention increased pupils' theoretical sleep knowledge and knowledge about good sleep practices. However, their actual sleep practices did only improve in a short-term period but then became worse. We suggest that interventions might be longer and should last over the whole school year.