Esther Mertens

| 63 Effectiveness of a Psychophysical Intervention Secondary outcomes. Students in the Light conditions showed more beneficial trajectories of change for self-control and emotional self-regulation compared to students in the Control condition (see Figure 3). The effect sizes were small for both outcomes (Cohen, 1988). Students in the Light condition showed a steeper increase in self-control (slope = 1.75) than students in the Control condition (slope = 1.44). Regarding emotional self-regulation, students in the Light condition improved over time (slope = .24), whereas students in the Control condition slightly declined (slope = -.10). For both outcomes, students improved most in the first year of the intervention. Furthermore, there was a trend suggesting that students in the Light condition had a slightly more beneficial trajectory for self-esteem than in the Control condition. Students in the Light condition remained relatively stable (slope = -1.68), whereas students in the Control condition showed a small decrease in self-esteem (slope = -2.58). Intervention effects were small (Cohen, 1988) with the strongest effect from T2 to T3, so in between the first and second year of the intervention. No intervention effects were found for self-reflection and for students in the Standard and Plus conditions (see the supplementary material for the slopes of all conditions and outcomes in the interpersonal domain). Again, the Light condition seemed to have the most beneficial growth trajectories for the secondary outcomes with most improvement early in the intervention. Discussion The purpose of the present study was, first, to examine whether a psychophysical intervention could positively affect prevocational students, a challenging group to involve in interventions, and, second, to determine the extent to which the width of an intervention’s ecological focus influences intervention effects. The psychophysical intervention R&W showed to be moderately effective in fostering some aspects of students’ intra- and interpersonal domains, but only when the ecological focus of the intervention was narrow. R&W Light was specifically effective in stimulating competencies and preventing problems in the intrapersonal domain (i.e., psychological wellbeing, sexual autonomy, and internalizing behavior). In the interpersonal domain, R&W Light showed a potential tendency to function as a buffer against declining positive interpersonal relations in the class and against increasing aggression and bullying. In addition, R&W showed small positive intervention effects on the secondary outcomes (i.e., self-control, emotional self-regulation, and a trend for self-esteem). Although intervention effects were small (when significant effects were found they ranged from .24 to .38), the observed effect sizes are consistent with effect sizes reported for other universal school-based interventions addressing the intra- and/or interpersonal domain (e.g., Cohen’s d = .22 – .27, Durlak et al., 2011; Cohen’s d = .10 – 25, Mertens et al., 2020). 3