Esther Mertens

114 | Chapter 6 In the present meta-analysis, we therefore examined the effects of universal secondary school-based interventions on students’ intrapersonal and interpersonal domains. School-based interventions addressing adolescents’ intra- and interpersonal domains typically show small positive effects (e.g., effect sizes (Cohen’s d ) ranging from .03 to .24; Dray et al., 2017; Durlak et al., 2011; Jiménez-Barbero, Ruiz-Hernández, Llor- Zaragoza, Pérez-García, & Llor-Esteban, 2016). One way to increase the effectiveness of interventions is by studying which components are related to intervention effects. By identifying components associated with stronger or weaker intervention effects, existing and new interventions can be optimized. In addition, schools can make informed decisions about which intervention to implement, by selecting interventions based on the evidence base for the components. As a first step towards cataloguing potentially effective components, Boustani and colleagues (2015) provided an overview of the components that are most frequently included in effective school-based interventions (e.g., problem solving, psychoeducation). Although such a frequency count provides a useful overview, it does not show whether the effectiveness of interventions are actually related to the presence of the components. Furthermore, due to the focus on effective interventions, the overview does not identify potentially ineffective or iatrogenic components. Therefore, the present meta-analysis identified which components are related to stronger intervention effects and which components are related to weaker intervention effects. In the literature, typically three types of components are distinguished: Content, instructional, and structural components. Content components are specific skills adolescents learn to promote positive outcomes, such as emotion regulation and problem solving (Boustani et al., 2015), i.e., “what do they learn.” Instructional components are techniques and methods of information delivery used by the intervention facilitator, such as cognitive restructuring and modeling (Boustani et al., 2015), i.e., “how do they learn it.” Structural components describe the structure of the intervention that might impact results, such as the number of sessions and whether or not parents are included in the intervention (Lee et al., 2014), i.e., “how is the intervention set up.” By examining all three types of components, we are able to unravel whether each type of components is equally important for intervention success or whether especially one type of components appears to be more important than others. There are various meta-analyses of intervention components that predict intervention effects (e.g., De Vries, Hoeve, Assink, Stams, & Asscher, 2015; Kaminski et al., 2008; Van der Put, Assink, Gubbels, & Boekhout van Solinge, 2018), but few meta-analyses have focused on components of school-based interventions. Meta- analyses that did examine components of school-based interventions focused on substance use, sexual risk behaviors (e.g., pregnancy, STD/HIV) and/or nutrition (see for a review of reviews Peters, Kok, Ten Dam, Buijs, & Paulussen, 2009). For example, Onrust, Otten, Lammers, and Smit (2016), focusing on substance use, found that in middle and high school components that sought to stimulate students’ self-control