5. Conclusions
Previous studies have advocated a need for interventions addressing the school environment to prevent stress among students. As part of the larger multi-component school-based HHS intervention to promote well-being (the primary outcome), educational and environmental strategies were developed to prevent stress among high school students (16-year-olds) in Denmark. In this study, we evaluated the effect of the HHS intervention on students’ perceived stress at a 9-month follow-up. We found no evidence of an effect of the intervention in the total study population nor in specific subgroups. The lack of effect may be due to the low implementation of several of the main stress preventive initiatives and limitations in the design of the intervention program; inducing a change in stress levels may require more intensive interventions. Future interventions targeting students in high schools should carefully consider including a feasibility study to identify challenges with implementing interventions and delivering trials in a high school setting. The descriptive data showed that half of students reported moderate or high levels of perceived stress. This highlights the continued need for effective interventions targeting stress among young people in Denmark. Future interventions could benefit from including the whole system of young people’s lives and focus more on several structural levels apart from just the school setting. An important next step for the HHS Study will be to evaluate the association between implementation and perceived stress in the intervention group and to examine the school-level characteristics of schools in groups of a high compared to a low implementation. These analyses can contribute further knowledge regarding the impact of the HHS intervention and help clarify whether the lack of effect was caused by an inadequate implementation or the poor quality of the intervention. 