Esther Mertens

96 | Chapter 5 reinforcement and its influence on the perceived classroom peer context. This is a unique approach as most studies examine these peer processes with questionnaires (e.g., Hofmann & Müller, 2018) or do not explicitly examine change in modeling and reinforcement within an intervention context (e.g., Dishion, Spracklen, Andrews, & Patterson, 1996). Second, we examined classmates’ influences in not self-selected dyads to broaden the ecological validity of previous findings regarding peer influences. Focusing on involuntary, not self-selected peer groups such as classmates enabled us to emphasize relationship quality and examine peer influence beyond selection effects (Juvonen & Ho, 2008). In addition, by randomly assigning students to dyads we included various types of relations between classmates capturing the broad range of possible relations within a class. This is important as adolescents are exposed to behaviors of all their classmates and not only a selective group of classmates (e.g., friends, popular students; Busching & Krahé, 2020). Third, we examined classmates’ deviant as well as prosocial modeling and reinforcement to unravel classmates’ influences on students’ perceptions of the classroom peer context, as recommended by Busching and Krahé (2020). By examining both deviant and prosocial modeling and reinforcement we could compare classmates’ negative influences with classmates’ positive influences as these might not be identical. Research examining classmates’ influences has often focused on either deviant or prosocial influences (e.g., Hofmann & Müller, 2018; Juvonen & Ho, 2008) eliminating the possibility to directly compare deviant with prosocial influences. Method Data for the present study were collected as part of a larger study examining the effectiveness of R&W which is approved by the Ethical Committee of the Faculty of Social and Behavioral Sciences of Utrecht University (FETC17-015; see for protocol Mertens, Deković, Van Londen, & Reitz, 2018). The trial is registered in the Dutch Trial Register, number NL6371 (NTR6554). Procedure Schools that offered a preparatory vocational education track and had not implemented R&W in the last two years were able to participate. The Dutch secondary school system consists of three educational tracks: Preparatory vocational education track, preparatory college education track, and preparatory university education track. These tracks are attended by respectively, 54%, 23%, and 23% of the total student population (Central Bureau for Statistics, 2020).