Esther Mertens

66 | Chapter 3 in different ways by other teachers or parents. Receiving various and, possibly, mixed messages could confuse students and push the intended intervention message to the background reducing the chance of students to benefit from the intervention. The results of the present study should be interpreted in light of its strengths and limitations. Strengths of the study were the longitudinal data, the three conditions differing in the width of ecological focus, and the large sample size. This enabled us to examine change in students over two years with different levels of ecological focus. A limitation is that R&W trainers did not report how teachers applied the intervention techniques during regular lessons, but only how often. Information about how intervention techniques were applied during regular lessons would have provided insight in possible mixed intervention messages. Hence, future research should also measure how intervention techniques are used outside the intervention lessons to examine whether differential implementation affects intervention effects. This knowledge can shed light if and to what extent implementation outside intervention lessons should be structured. Second, the R&W trainers were providing the intervention for the first time, after three days of training. More experienced trainers might be able to establish more change. On the other hand, using first time trainers ensured that trainers in our study were comparable concerning their experience with the intervention. Last, we examined intervention effects immediately following the intervention. Future research should analyze follow-up data to examine long term effectiveness of the intervention. Conclusion Prevocational students seem to be most in need of an effective intervention to positively stimulate their competencies and prevent the development of problems in both the intra- and interpersonal domain, but might be at the same time a challenging group of students to target. Our study showed that an intervention using a psychophysical approach can positively affect prevocational students. The intervention was especially effective in targeting students’ intrapersonal domain and showed the strongest, albeit small, effects in the first year. In the interpersonal domain, the intervention potentially functions as a buffer. R&W showed a tendency to lessen the decline in positive interpersonal relations in the class and the increase in levels of aggression and bullying. Furthermore, the present study showed that intervention effects do not per definition increase with a longer intervention or a broader ecological focus; strongest intervention effects were shown in the first year and when the intervention had a narrow ecological focus. The finding that “less is more” has important implications for the practice as it indicates that it might not always be worthwhile for schools to invest in implementing a long-term intervention with a broad ecological focus.