Esther Mertens

Abstract Background: Students following a preparatory vocational education track seem most in need of an intervention stimulating their competencies and preventing the development of problems in the intrapersonal and interpersonal domain. At the same time, these students are a challenging group to involve in interventions. The aim of the present study was to examine, first, whether a 2-year intervention using a unique combination of a physical approach with a more common psychological approach (i.e., a psychophysical approach) is effective in improving students’ competencies and preventing problems in the intra- and interpersonal domain, and, second, whether the width of the ecological focus of the intervention influenced its effectiveness. Methods: We conducted a Randomized Controlled Trial with a sample of 7 th Grade students ( N = 1299, M age  = 12.38, 54% boys). Students reported on outcomes of the intra- and interpersonal domains using digital questionnaires. The data was analyzed with Latent Growth Curve models. Results: Results showed that the intervention was most effective when implemented with the most narrow ecological focus (i.e., only a core team of teachers involved in the intervention) and improved several outcomes in students’ intrapersonal domain, interpersonal domain, and secondary outcomes (self-control and emotional self- regulation). The intervention effects were strongest, albeit small, in the first year of the intervention. Conclusion: These results show that interventions with a psychophysical approach and a narrow ecological focus might be promising interventions for prevocational students, although effort should be put in increasing its effectiveness. Trial registration: Dutch Trial Registration number NL6371 (NTR6554). Registered 3 July 2017. Keywords: School-based intervention; randomized controlled trial (RCT); intrapersonal domain; interpersonal domain; implementation 44 | Chapter 3